ng as their respective bases Chester,
Shrewsbury, and Gloucester. But though there is some evidence of an
organised plan for the conquest of Wales in the time of William Rufus,
it is useless to look for any great and general system of offence or
defence, because most of the castles were not built by a centralised
government with any such object in view, but by individuals to guard
their own territories and protect their independence against either
their neighbours or the English king. The great age of castle-building
was between 1100 and 1300. Castles play a very small part in the
fighting in Wales till the end of the eleventh century. Before that
time indeed there were few stone castles anywhere; the usual type, even
of the early Norman castles, was a moated mound surrounded by wooden
palisades. One hears for instance of a castle being built by William
the Conqueror in eight days. An example of this early type of fortress
was Pembroke Castle at the end of the eleventh century, "a slender
fortress of stakes and turf," which had the good fortune to be in
charge of Gerald of Windsor, grandfather of Giraldus Cambrensis. It
stood several sieges, which shows that the siege engines of the Welsh
were of a very poor and primitive type. One of these sieges was turned
into a blockade, and the garrison was nearly reduced by starvation. The
constable had recourse to a time-honoured ruse. "With great prudence he
caused four hogs which still remained to be cut into small pieces and
thrown down among the enemy. The next day he had recourse to a more
refined stratagem: he contrived that a letter from him should fall
into the hands of the enemy stating that there was no need for
assistance for the next four months." The besiegers were taken in and
dispersed to their homes.

The characteristic types of castles in the twelfth century were the
rectangular keep and the shell keep; in the thirteenth the concentric
castle. Of the two last we have splendid examples in Cardiff and
Caerphilly. Of rectangular keeps there are very few in Wales--Chepstow
is the only important one--though there are several on the borders,
notably Ludlow. The square keep seems to us most characteristic of
Norman military architecture; the Tower of London, Rochester,
Newcastle, Castle Rising, are well-known examples, and there are many
more in a good state of preservation; there are many more solid square
keeps than shell keeps well preserved, but this is simply due t