Beginning at the end of the eleventh century, the Crusades introduced Europeans to sophisticated Byzantine and Muslim military architecture and ushered in a new phase of castle building. As long as wars were fought with poorly trained and undisciplined troops, and when battles were short, bloody encounters between mobs going at each other in hand-tohand combat, the great tower and its walled enclosure made an effective castle. As siege techniques and equipment changed and troops of archers and teams of siege engineers joined knights trained for single combat, the castle design had to change to meet the new challenge (see Chapter 2). Pembroke, on the south coast of Wales, was founded by Normans in 1093–94 (see Figures 3 and 4). The great round tower from the end of the twelfth century shows a marked improvement in military engineering over the square plan of earlier towers. With no corners to batter or mine and of masonry throughout, the round tower was a significant improvement on the earlier cubical buildings.