Depends on the period. Part of the problem is that the popular imagination tends to see the Middle Ages as a uniform period of technological stagnation, when in

Depends on the period. Part of the problem is that the popular imagination tends to see the Middle Ages as a uniform period of technological stagnation, when in fact there was great change and progress throughout the period. Early medieval castles were indeed wood-and-earthworks fortifications, but stone castles were active fortifications for a long time that would be considered "middle ages".