Following the Roman Empire's invasion of southern Britain, the mining of lead and silver in the Mendip Hills provided a basis for local industry and commerce. Bath became the site of a major Roman fort and city, the remains of which can still be seen. During the Early Medieval period Somerset was the scene of battles between the Anglo-Saxons and first the Britons and later the Danes. In this period it was ruled first by various kings of Wessex, and later by kings of England. Following the defeat of the Anglo-Saxon monarchy by the Normans in 1066, castles were built in Somerset.