The pointed arch so characteristic of Europe’s Gothic cathedrals was an invention borrowed from Islamic architecture. It was much stronger than the rounded arch used by the Romans and Normans, thus allowing the building of bigger, higher, more complex and grander buildings. Other borrowings from Muslim genius included ribbed vaulting, rose windows and dome-building techniques. Europe ‘s castles were also adapted to copy the Islamic world’s – with arrow slits, battlements, a barbican and parapets. Square towers and keeps gave way to more easily defended round ones. Henry V’s castle architect was a Muslim.