FASCICULI ARCHAEOLOGIAE HISTORICAE

FASC. XXXIII, PL ISSN 0860-0007

DOI 10.23858/FAH33.2020.006

CHRISTOF KRAUSKOPF*, PETER PURTON**

FROM THE TOWER TO THE BASTION.

CHANGES IN FORTRESS DESIGN TO ACCOMMODATE
GUNPOWDER ARTILLERY (14TH TO 16TH CENTURIES)

Abstract: The authors set out the key turning points in the evolution of defensive architecture in response to the appearance of firearms
in the 1st quarter of the 14th century in Europe, for both attack and defence. Between the first adaptations to defences during the middle of
the 14th century to the emergence of geometric whole defensive systems based on low-lying bastions and interconnected outworks in the
16th century, there was a long period of evolution, experimentation and development, responding to continuous improvement in the range
and destructive power of gunpowder artillery. New designs of castles, fortresses and town walls focussed on the need to shield high medie-
val walls and towers against the power of the gun, but also on how to mount guns on defences and integrate loop holes to keep an attacker
as far away as possible. Ideas diffused rapidly across Europe and the Muslim world. Factors such as the builder’s wealth and the purpose of
the fortress also determined what was constructed.

Keywords: Europe, firearms, defensive architecture, castle, fortress, loop hole

Received: 31.03.2020 Revised: 24.04.2020 Accepted: 27.05.2020

Citation: Krauskopf C., Purton P. 2020. From Tower to the Bastion. Changes in Fortress Design to Accommodate Gunpowder Artillery
(14th to 16th Centuries). “Fasciculi Archaeologiae Historicae” 33, 89-101, DOI 10.23858/FAH33.2020.006

It took up to two hundred years to progress from the ruling class was international and so were medieval
first confirmed appearance of gunpowder weapons in engineers.1 Technological change diffused rapidly. It
Europe and the Middle East to the first new fortifications is rare that we can prove which country or which ruler
wholly designed according to geometric principles and was the first to make something wholly new.
based on the use of low-lying, interlocking bastions and There is, however, good evidence to suggest that
outworks to defend against and to mount artillery. the first changes to fortifications to accommodate the
The authors are researching this long process in de- new weapon were made in England, during the Hun-
tail, to explore how and when changes were made in dred Years War with France. This fits well with the evi-
fortress design, but also what inspired such develop- dence that gunpowder was first used in war in Europe
ments and how effective they were. One challenge is in the early 14th century. The English used guns at the
that there are thousands of examples across the Chris- battle of Crécy in 1346 and at the siege of Calais imme-
tian and Muslim worlds; the second is that there is un- diately after, although with little effect. The first datable
certainty about dating many of them. This paper sug- evidence of fortifications being adapted so that the de-
gests a few critical turning points (Fig.1). fenders could use these small and inaccurate weapons
One thing is clear at the start. Wherever a change was was at the abbey of Quarr on the Isle of Wight, which
made, it did not remain private for long. The medieval was subject to seaborne attacks by the French, when
a  wall was built with two square holes cut through it
*
Brandenburgisches Landesamt für Denkmalpflege und Archäo- (Fig. 2), in 1365.2 The gun must have sat on a timber
logisches Landesmuseum; https://orcid.org/0000-0002-7362-934X;
christof.krauskopf@bldam-brandenburg.de
**
Independent scholar, London UK; https://orcid.org/0000- 1 
See Purton 2018, passim.
0002-7215-7125; purtonpeter@gmail.com 2 
Renn 1968, 301-302.

89
 CHRISTOF KRAUSKOPF, PETER PURTON

Fig. 1. Map of locations of the sites mentioned in the text. Map C. Krauskopf, BLDAM: Brandenburgisches
Landesamt für Denkmalpflege und Archäologisches Landesmuseum.

trestle. Possibly even earlier, 1347, although this date that firearms were quite common in the 2nd half of the
is not definite, were the holes built into the wall of the 14th century all over Europe. But firearms still had little
rich city of Norwich3 which are also small, and crude effect, as we can see from many sources. In a document
(Fig. 3). from 1395 concerning the liberation of the King of
Soon after, fortresses are found where holes cut into Sweden and his son from captivity in Denmark, north-
walls for the use of guns became part of the design it- ern German towns had to deliver firearms – but only
self. In England and France there are many examples four cannons and six guns together with the amount of
from castles and town defences built in the 1370s and gun powder required for the weapons. But they had to
1380s. These were usually circular loops for the gun provide 300 marksmen with good crossbows! That may
at the end of vertical sighting slits, often using a tim- shed a light on the significance of firearms until the end
ber base on a stone sill for resting the gun. However, of the 14th century.5
the design of the wall or tower was not changed from The next turning point was to move from inserting
traditional forms. At this time, it appears, no one was new gun ports in existing defences to specifically de-
concerned that the guns of the attacker could damage signing gun towers, sometimes newly built, sometimes
the masonry, it was only about using the gun to defend adapted, which become larger and stronger through the
from the inside. Figure 4 is a  small baron’s castle at 15th century. One of the first may be also from England,
Cooling in Kent built in 1381. It may be a status sym- the ‘God’s House Tower’ built at Southampton not later
bol although the English peasants’ revolt and similar than 1417 (Fig. 5), again in response to the threat of
loops at other contemporary fortifications in this region seaborne attack. This projecting tower allowed guns at
(south east England), such as the major works on the two levels to fire in all directions from secure positions,
city wall of Canterbury, suggest another context. The sitting on the ground or the roof, behind thick walls.6
royal chief engineer, Henry Yevele, was involved in all The gun tower rarely stood alone. Alongside the
these works.4 tower, which might be round, rectangular or square,
The evidence for adapting defensive architecture many rulers across Europe turned to the erection of ad-
to the new weapons is quite rare – despite of the fact ditional external defences, sometimes of earth, some-
times masonry, or both, to shield the old towers and
3 
Ayers 1994, 65.
4 
Harvey 1944, 36, 38-39; Renn 1982, 117-118; Tatton-Brown 5 
MUB 1907, 535.
1985. 6 
O’Neil 1960, 11; Saunders 2000, 53-58.

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 FROM THE TOWER TO THE BASTION. CHANGES IN FORTRESS DESIGN…

Fig. 2. Quarr Abbey, Isle of Wight. Wall and gun loops, 1365. Photo P. Purton.

Fig. 3. Norwich (Norfolk): loops in St. Stephen’s Gate, possibly 1347. Photo P. Purton.

walls from the increasing effectiveness of guns as a re- shot weighing 50 to 100 kg. Examples of shield walls
sult of technological progress in metallurgy and im- are found in the mid-14th century in Germany, a region
provements in the manufacture of gunpowder itself, where the manufacture of guns and gunpowder was be-
which meant that by around 1400 for the first time coming a major industry.7
larger guns now posed a  threat to stone defences and
there are increasing references as the 14th century pro- The German term Schildmauer describes parts of the curtain
7 

gressed to bombards demolishing stretches of wall with wall which are taller and thicker than the rest of the curtain wall.

91
 CHRISTOF KRAUSKOPF, PETER PURTON

Teutonic Order there exists only one other example, the

castle of Świecie (former Schwetz), which dates between
1335 and 1350.12 The innovation of Bytów is the three
round corner towers, equipped for the use of handguns
with hooks. Today partially heavily restored, originally
the lower floors were open to the castle’s yard. Different
sizes and shapes of gun loops indicate that the builder
experimented with the new forms of defensive architec-
ture13 – as is to be seen in other buildings of the early and
middle 15th century.14 The towers differ very much com-
pared with roundels and battery towers of the 15th cen-
tury, they are very slim and still in a  “medieval tradi-
tion”. Another example of these early gun towers can be
seen in the corner tower of the castle of Greiffenberg in
Brandenburg. It is equipped with narrow gun loops in the
top floor. The loops could only be used with guns with
quite long barrels, hooked on a wooden bar, built in the
rear part of the opening (Fig. 7). It is not possible to date
the tower more precisely. It belongs according  to  pre-
sent knowledge to the third building phase, dating to the
2nd half of the 14th or 1st half of the 15th century.15 Assum-
ing that the loops belong originally to the tower, it seems
impossible that the building existed before 1400.16
Gun towers began to spread quickly after the earliest
Fig. 4. Cooling castle (Kent), built 1381 – gun loops. examples in Britain. The Hussite wars in Bohemia led
Photo P. Purton. to significant developments as many fortifications were
modernised. For a long time, Tábor was hailed as an ear-
On the continent as in Britain, high slim towers, ly example of gun towers built from the 1420s, but this
still in older defensive traditions, with loops for hand- dating, especially for the Kotnov tower, has now been
guns were erected. According to the account books the challenged.17 The town was fortified with an outer ward18
castle in Bytów (former Bütow) in the territory of the with polygonal gun towers. One of the oldest gun towers
Teutonic Order in Prussia was built between 1399 and in Bohemia existed in Worlik (Orlík nad Vltavou).19
14068 (Fig. 6). The account books allow the reconstruc- The impact of the Hussite wars led to the construc-
tion of the building process to be followed in detail. The tion of gun towers in neighbouring regions such as
measurements of the completed masonry served as ba- Franconia. Several examples have been discovered by
sis for payments to the masons and other crafts.9 Bytów Joachim Zeune, such as the towers at Altenstein with
seems to be a very early example and unique in the ter- inversely arranged T-shaped gun loops or Lichtenstein,
ritory of the Teutonic Order during that period. Chris- both dated to the time around 1430.20
tofer Hermann is of the opinion that master John, who
constructed the extension of the Grand Masters palace
of the Malbork (former Marienburg) beginning around
12 
Herrmann 2011, 162.
13 
Herrmann 2011, 162.
1380, also worked at Bytów.10 The castle was a  com- 14 
See below, especially on the Castle Eisenhardt in Bad
pletely new construction with a unique plan compared to Belzig.
the other castles of the Teutonic Order in that region. It 15 
Chantre and Rathgeber 2008, 26, Figs. 27 and 30.
comes back to a well-tried composition, common in west 16 
During the analysis by Christiane Chantre and Julia Rathge-
Europe and Bohemia since the 12th century, the quad- ber it was not possible to examine the corner tower in detail.
17 
Varhaník 1997; Durdík 2000; Durdík 2007, 38-39.
rangular castle with corner towers.11 In the lands of the 18 
Outer ward is here used for the German term Zwinger, mean-
ing the space in front of the main curtain wall, which is sheltered
by a second, in most cases lower wall, often equipped with flanking
Shield walls cover buildings and parts of castles against bombard- towers. The terms lower or outer bailey are also used as translation
ment with trebuchets, and, from the 15th century, cannons. for Zwinger, but describe a different phenomenon. Even outer ward
8 
Herrmann 2011, 160-162. may mean more than what is described by the term Zwinger. In the
9 
For details see especially Lemcke 1911, 153-158. area of the Teutonic Order, the term Parcham is used.
10 
Herrmann 2019, 398, 411. 19 
Varhaník 1998, 31, Figs. 8-12.
11 
Durdík 1994; Schicht 2003. 20 
Geibig and Zeune 2003, 184-186; Zeune 2011, 76-77.

92
 FROM THE TOWER TO THE BASTION. CHANGES IN FORTRESS DESIGN…

Fig. 5. Southampton (Hampshire), city walls. The ‘God’s House Tower’, built by 1417. Photo P. Purton.

Fig. 6. Bytów (Poland), front of the castle with two guntowers. Photo C. Herrmann.

Lichtenstein is especially interesting. Between storey prove the use of guns equipped with hooks. In
1417 and 1436 1000 gulden were invested in two gate- a  document from 1430, issued by the bishop Johann
houses and a gun tower in the so called Nordburg and of Würzburg concerning the building activities in his
an outer ward in the Südburg. The loops in the gun castle Lichtenstein, he mentions the reasons for the
tower were first interpreted as arrow loops construct- works: “[…] the infidel damned heretics from Bohemia
ed for the use of longbows as they are 3 m long and [...] therefore it is very important to fortify towns and
20 cm wide. But thorough investigation revealed that castles in this country.”21
the loops were constructed for two marksmen on two
levels (Fig. 8). Traces of horizontal timber beams on Zeune 2011, 76. The source is partially edited by Bodo
21 

the two levels and at the shorter gun loops in the upper Ebhardt (1901, 173).

93
 CHRISTOF KRAUSKOPF, PETER PURTON

Fig. 7. Greiffenberg (Brandenburg), gun loop on the corner tower. Fig. 8. Lichtenstein (Franconia), reconstruction of the interior gun
Photo C. Krauskopf, BLDAM. tower. Drawn R. Mayrock, Büro für Burgenforschung J. Zeune.

One major means of defence very quickly be- combined with gun towers, as in the Trendelburg in
came the attempt to keep the attacker away from the Hesse24 (Fig. 9). Not before the late 15th century the
inner defences. Two older concepts, the outer ward, dimensions of shield walls changed at the time of the
and the shield wall, were adapted to the new defence impact of heavy firearms, as in Neu-Scharfeneck in
systems. Germany. The shield wall of Helfštýn (Helfenstein)
Shield walls should prevent attackers from caus- in Moravia shows two segmented arched projec-
ing damage to the castle buildings with missiles tions.25 In many cases shield walls were combined
thrown into the castle. A very impressive example is with gun towers as in the Hohkönigsburg in Alsace26
preserved in the Farnsburg near Basel.22 The wall dat- or Worlik (Orlík nad Vltavou) and maybe also Výrov
ing to the mid-14th century is 3 m thick and about 8 m in Bohemia.27
high. Often shield walls were not that thick, they im- The older examples of outer wards from the late
pressed visually but might not have enough strength 13th and the 14th centuries were often not very thick
to withstand attacks with trebuchets. The impact of walls with flanking towers, encircling the inner cas-
the missiles of bombards and cannons in the 2nd half tle at a short distance.28 A well-known example is the
of the 15th century was much stronger than that of outer ward of the castle of Prague. The construction
trebuchets. Nevertheless, even old shield walls could
withstand bombardments with cannons – the already
mentioned wall of the Farnsburg was bombarded for 24 
Friedhoff 2011, 69-70; Brohl 2013, 189-194; Strickhausen
three weeks in 1444 without success.23 Newly-erected and Strickhausen 2015.
shield walls were often equipped with gun loops and
25 
Durdík and Bolina 2001, 193.
26 
Uhl and Zeune 1999, 234.
27 
Orlík: Varhaník 1998, 31, Fig. 15; Výrov: Durdík 2005, 164.
22 
To the Farnsburg see Meyer 1981, 94-97; Schmaedecke 2005.
28 
To the outer ward in general and to its effectiveness see Gut-
23 
Meyer 2009, 241 and footnote 25. bier 1976; Müller and Schmitt 2007; Meyer 2009.

94
 FROM THE TOWER TO THE BASTION. CHANGES IN FORTRESS DESIGN…

Fig. 9. Trendelburg (Hesse). Redrawing after Atlas 1967, 33B, Fig. 11. Wenecja (Poland). After Salm 2011, Fig. 11.
Photo C. Krauskopf, BLDAM.

various other examples, such as Kollenberg in Fran-

conia with a polygonal outer ward with rectangular
flanking towers (Fig. 10). The castle has a very early
example of a  caponier, built in connection with the
outer ward also around 1430.30
The new types of outer wards became a  critical
part of defensive architecture. Newly-built castles
in the late 14th century often still lack this important
part. Landgrave Hermann II of Hesse built Hermann-
stein near the town of Wetzlar from 1376 against
Count Johann IV of Solms-Burgsolms who had taken
the town in that year. The castle – specially erected
in a conflict – consisted of a big donjon with nearly
no defensive features.31 A  comparable concept was
followed while refortifying the Weidelsburg. Land-
grave Hermann II and the count of Waldeck agreed
to rebuild the older ruined castle and to equip it with
troops and weapons. But they built only a  big don-
jon – the outer ward with inverted keyhole gun loops
Fig. 10. Kollenberg (Franconia). After Feulner 1913, Fig. 35. dates to the 1420s or ‘30s.32
During the first decades of the 15th century the con-
struction of outer wards became common. In many
began in 1370, when Emperor Charles IV decided parts of central Europe, they were erected around older
to strengthen the southern defences of the castle.29 castles. There are countless examples in central Europe,
In the 15th century new outer defences with flank- one of the most famous being in Malbork,33 others in
ing, powerful, gun towers were erected by the en-
gineer Benedikt Ried on the south and north sides.
Tábor has already been mentioned, but there are 30 
Feulner 1913, 59-69; Zeune 2011, 81-82.
31 
Gutbier 1973, 158-163; Friedhoff 2011, 63-64.
32 
Gutbier 1999, 155; Friedhoff 2011, 64; Knöppel 2017.
29 
Chotěbor 2007, 161. 33 
Pospieszny 2007 with further mentions of older literature.

95
 CHRISTOF KRAUSKOPF, PETER PURTON

Fig. 12. Castle Eisenhardt, Bad Belzig (Brandenburg). Redrawing of a plan of the Royal Government Potsdam
by building officer Köhler, 1890 and photos of the three northern towers. Photo C. Krauskopf, BLDAM.

Fig. 13. Zossen (Brandenburg), battery tower. Fig. 14. Gerswalde (Brandenburg), guntower.
Photo D. Möller, BLDAM. Photo C. Krauskopf, BLDAM.

Wenecja in central Poland (Fig. 11)34 or Schweinsberg cannon ports. The first fortresses as complete defensive
in Germany, the last example connected to the master systems were erected and that happened all over Eu-
builder Hans Jakob von Ettlingen.35 rope during a very short time.
From the mid-15th century a similar defensive con- Honberg near Tuttlingen, built from about 1460 on,
cept was established. Very strong walls were erected is regarded as the first fortress in Württemberg.36 Also
to fortify new places or encircle older castles. They since the 1460s the electoral princes of Saxony began to
were equipped with big gun towers, evoking the flank- refortify the castle mount of Belzig, situated on the north-
ing or corner towers attached to the outer ward – but ern border against the principality of Brandenburg.37
they were much stronger buildings with gun loops and
Ottersbach et al. 2014, 135ff.
36 

34 
Salm 2011, 151. Bergmann 2005; Langer 2007; Langer 2011; Krauskopf
37 

35 
Gutbier 1973, 134-157; Ottersbach 2015, 197, Fig. 17. 2011, 54-55; Gebuhr 2018.

96
 FROM THE TOWER TO THE BASTION. CHANGES IN FORTRESS DESIGN…

Fig. 15. Auxonne (Côte d’Or). Embrasure in the foot of the gun Fig. 17. Dubrovnik (Croatia). Minčeta tower and surrounding
tower, covering ditch and entrance. Photo P. Purton. outer wall and curtain rebuilt by Michelozzo from 1461.
Photo P. Purton.

as in the examples of Greiffenberg and Gerswalde in

Brandenburg39 (Fig. 14).
But with the growing effectiveness of cannons, the
question of how to keep attackers further away, while
also being able to flank the curtains effectively, became
a dominant concern for designers of fortresses. The ans-
wer, we now know, was the low-lying fortress with
interconnecting bastions for mounting guns combined
with large scale linked outworks but hindsight is the
enemy of good history and this solution was not obvi-
ous in the 15th century. Instead we find large numbers
of new fortresses that tried to resolve the problems with
different solutions. The decades from 1450 to 1510 were
a time of transition and experimentation. Many books
Fig. 16. Ostia, near Rome. Fortress, built mid-1480s.
were written during this time advancing solutions to
Photo P. Purton.
the questions posed by modern artillery but only a few
were acted on by rulers, maybe they preferred what
Evidently the architects experimented with different they knew from practice or maybe they could not afford
concepts for the five big gun towers. They created to build the designs of Giotto, Taccola, Alberti, Filarete,
different gun loops, from long slits in a conical tower Giorgio Martini or Leonardo da Vinci.40
to round or mouth shaped loops in cylindrical towers The gun tower remained central in practice. Louis
(Fig. 12). The electoral princes of Brandenburg be- XI of France conquered Burgundy in 1477 and built
gan to build their first fortress later. At the end of the his ‘three sisters’, enormous new fortresses to secure
15th  century they erected – comparable with Belzig the province. One remains, at Auxonne (Fig. 15), where
– a  fortification with horseshoe-shaped gun towers the plan is a  pentagon and there are two gun towers
around the older castle of Zossen on the southern with walls five metres thick and ravelins in front of
border of their territory. Only one of the gun towers each gate.41 Not a new design, but the strongest of the
survives today (Fig. 13).38 current, perhaps?
Of course, not every nobleman could afford to build Much that was new was built in Italy and many sur-
fortresses like the Counts of Württemberg or the elec- vive today. Here there is space only to mention Ostia
toral princes of Saxony and Brandenburg. So, many
castles were strengthened only with single gun towers 39 
Greiffenberg: Chantre and Rathgeber 2008; Gerswalde:
Krauskopf 2011, 54.
40 
Purton 2010, 358-362.
38 
Krauskopf 2011, 56; Cante 2015. 41 
Mesqui 1997, 37-40.

97
 CHRISTOF KRAUSKOPF, PETER PURTON

Fig. 18. Salses (Pyrénées orientales), 1497: ditch, caponier and corner towers with talus added after failed French
siege 1503. Photo P. Purton.

Fig. 19. Rhodes. Medieval walls, ditch and tenaille from St. Athanasios tower. Photo P. Purton.

(Fig. 16), near Rome, which dates to the mid-1480s: examples of what would become the solution. Here, the
an irregular triangle, round towers at two corners but threat of Ottoman artillery had been well recognised
a  bastion at the point, a  continuous corridor inside since the fall of Constantinople in 1453 and was con-
and many gun positions, but it still had a donjon and tinuous. Dubrovnik’s defences were regularly updat-
machicolations.42 Southern Europe offers the clearest ed over many decades (Fig. 17) – the older Minčeta
tower stands inside casemates with walls six metres
42 
Verdier 1939, 282-316; Hale 1983, 9, 16. Other examples
from these decades include Brancaleone (Ravenna, 1457-1470), 1477), Brolio (Arezzo, 1484), and Sarzana (1487) and Sarzanello
Volterra (Pisa) and Imola (Bologna, both 1472), San Leo (Rimini, (1493, La Spezia).

98
 FROM THE TOWER TO THE BASTION. CHANGES IN FORTRESS DESIGN…

Fig. 20. Navarrenx (Pyrénées Atlantiques), bastion fortress built by Italian engineer 1530s. Photo P. Purton.

thick built from 1461, numerous gun positions, a wide Not yet a complete early modern fortress, but recognis-
ditch and outworks.43 Near Perpignan, now in southern ably closer.
France but then in Aragon, stands the fortress of Salses The 16th century saw the introduction of the modern
(Fig. 18) – built from 1497 to oppose the French, this fortress with bastions. Italian engineers in particular
is quadrangular and low lying with bastions – though were hired all over Europe to plan modern fortresses
not pentagonal – for guns, very thick walls, a caponi- with bastion systems as at Navarrenx (Fig. 20) built in
er, outworks: it is a genuine forerunner of later designs the Pyrenees by an engineer from Verona in the 1530s,
despite clinging onto a tall donjon for the governor.44 and in the 2nd half of the 17th century also in Peitz in
In 1500, there were fortresses with pentagonal bas- Brandenburg by Francesco Chiaramella around 1560,
tions attached, but none were yet integrated into an and later – 1590 – Rocco Conte di Linari at Küstrin
overall design. The nearest probably are the works to (Kostrzyn).
strengthen Rhodes after the failed Ottoman siege of 1480 There is much more detail to add and many more
(Fig. 19). The bastions of Rhodes are of different shapes questions to pose and to answer, this paper has merely
and sizes, and as important perhaps were the steps to cre- proposed the key turning points over a period of almost
ate outworks shielding the medieval walls, the thick- two centuries in which artillery, and fortifications, were
ening of those walls, an enormous ditch and the cre- transformed forever from the medieval to the early
ation of gun platforms to keep an enemy at distance.45 modern world.

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