New book claims these are the 10 greatest changes of the last 1,000 years

11th century: Castles

Most people think of castles as representative of conflict. However, they should be seen as bastions of peace as much as war. In 1000 there were very few castles in Europe – and none in England. This absence of local defences meant that lands were relatively easy to conquer – William the Conqueror’s invasion of England was greatly assisted by the lack of castles here. Over the 11th century, all across Europe, lords built defensive structures to defend them and their land. It thus became much harder for kings to simply conquer their neighbours. In this way, lords tightened their grip on their estates, and their masters started to think of themselves as kings of territories, not of tribes. Political leaders were thus bound to defend their borders – and govern everyone within those borders, not just their own people. That’s a pretty enormous change by anyone’s standards.