Castle building began in earnest in Europe in the 11th century. Some were simple, wooden buildings with a fence and ditch around them for protection. Motte-and-bailey castles were more complex and had a big advantage - height. The bailey or courtyard was where animals were kept and it would contain stables, workshops and a chapel. A motte was important for castle defence. By piling up earth and building the castle tower on top, people inside could see an attacking army coming from far away.