At this stage the crusades, and the consequent opportunities afforded to
western engineers of studying the solid fortresses of the Byzantine
empire, revolutionized the art of castle-building, which henceforward
follows recognized principles. Many castles were built in the Holy Land
by the crusaders of the 12th century, and it has been shown (Oman, _Art
of War: the Middle Ages_, p. 529) that the designers realized, first,
that a second line of defences should be built within the main
enceinte, and a third line or keep inside the second line; and secondly,
that a wall must be flanked by projecting towers. From the Byzantine
engineers, through the crusaders, we derive, therefore, the cardinal
principle of the mutual defence of all the parts of a fortress. The
_donjon_ of western Europe was regarded as the fortress, the outer walls
as accessory defences; in the East each envelope was a fortress in
itself, and the keep became merely the last refuge of the garrison, used
only when all else had been captured. Indeed the keep, in several
crusader castles, is no more than a tower, larger than the rest, built
into the enceinte and serving with the rest for its flanking defence,
while the fortress was made strongest on the most exposed front. The
idea of the flanking towers (which were of a type very different from
the slight projections of the shell-keep and rectangular tower) soon
penetrated to Europe, and Alnwick Castle (1140-1150) shows the influence
of the new system. But the finest of all castles of the middle ages was
Richard Coeur de Lion's fortress of Chateau Gaillard (1197) on the Seine
near Les Andelys. Here the innermost ward was protected by an elaborate
system of strong appended defences, which included a strong
_tete-de-pont_ covering the Seine bridge (see Clark, i. 384, and Oman,
p. 533). The castle stood upon high ground and consisted of three
distinct enceintes or wards besides the keep, which was in this case
merely a strong tower forming part of the innermost ward. The donjon was
rarely defended _a outrance_, and it gradually sank in importance as
the outer "wards" grew stronger. Round instead of rectangular towers
were now becoming usual, the finest examples of their employment as
keeps being at Conisborough in England and at Coucy in France. Against
the relatively feeble siege artillery of the 13th century a well-built
fortress was almost proof, but the mines and the battering ram of the
attack were more formidable, and it was realized that corners in the
stonework of the fortress were more vulnerable than a uniform curved
surface. Chateau Gaillard fell to Philip Augustus in 1204 after a
strenuous defence, and the success of the assailants was largely due to
the wise and skilful employment of mines. An angle of the noble keep of
Rochester was undermined and brought down by John in 1215.
[Illustration: FIG. 5.--Krak-des-Chevaliers: View.]
[Illustration: FIG. 6.--Chateau Gaillard.
A. _High Angle Tower_
B.B. _Smaller Side Towers_
C.C. D.D. _Corner Towers_
E. _Outer Enceinte, or Lower Court_
F. _The Well_
G.H. _Buildings in the Lower Court_
I. _The Moat_
K. _Entrance Gate_
L. _The Counterscarp_
M. _The Keep_
N. _The Escarpment_
O. _Postern Tower_
P. _Postern Gate_
R.R. _Parapet Walls_
S. _Gate from the Escarpment_
T.T. _Flanking Towers_
V. _Outer Tower_
X. _Connecting Wall_
Y. _The Stockade in the River_
Z.Z. _The Great Ditches_]
The next development was the extension of the principle of successive
lines of defence to form what is called the "concentric" castle, in
which each ward was placed wholly within another which enveloped it;
places thus built on a flat side (e.g. Caerphilly Castle) became for the
first time more formidable than strongholds perched upon rocks and
hills such as Chateau Gaillard, where the more exposed parts indeed
possessed many successive lines of defence, but at other points, for
want of room, it was impossible to build more than one or, at most, two
walls. In these cases, the fall of the inner ward by surprise, escalade,
_vive force_, or even by regular siege (as was sometimes feasible),
entailed the fall of the whole castle.
[Illustration: FIG. 7.--Coucy: Plan.]
[Illustration: FIG. 8.--Coucy: View.]
The adoption of the concentric system precluded any such mischance, and
thus, even though siege-engines improved during the 13th and 14th
centuries, the defence, by the massive strength of the concentric castle
in some cases, by natural inaccessibility of position in others,
maintained itself superior to the attack during the latter middle ages.
Its final fall was due to the introduction of gunpowder as a propellant.
"In the 14th century the change begins, in the 15th it is fully
developed, in the 16th the feudal fastness has become an anachronism."
The general adoption of cannon placed in the hands of the central power
a force which ruined the baronial fortifications in a few days of
firing. The possessors of cannon were usually private individuals of the
middle classes, from whom the prince hired the _materiel_ and the
technical workmen. A typical case will be found in the history of
Brandenburg and Prussia (Carlyle, _Frederick the Great_, bk. iii. ch.
i.), the impregnable castle of Friesack, held by an intractable feudal
noble, Dietrich von Quitzow, being reduced in two days by the elector
Frederick. I. with "Heavy Peg" (_Faule Grete_) and other guns hired and
borrowed (February 1414). The beginnings of orderly government in
Brandenburg thus depended upon the guns, and the taking of Friesack is,
in Carlyle's phrase, "a fact memorable to every Prussian man." In
England, the earl of Warwick in 1464 reduced the strong fortress of
Bamborough in a week, and in Germany, Franz von Sinkingen's stronghold
of Landstuhl, formerly impregnable on its heights, was ruined in one day
by the artillery of Philip of Hesse (1523). Very heavy artillery was
used for such work, of course, and against lighter natures, some castles
and even fortified country-houses or castellated mansions managed to
make a stout stand even as late as the Great Rebellion in England.
[Illustration: From Clark's _Med. Mil. Arch._