After the Roman conquest of Britain in 43 CE they built a number of forts to impose their authority. They included one built inside the earlier Iron Age hill fort at Ham Hill, one at Charterhouse on the Mendip Hills, and probably another at Ilchester where a settlement developed around an important crossroads and river crossing. While earlier trackways continued to be used, a number of relatively straight, well drained Roman roads were built to facilitate communications between the forts and allow the rapid movement of troops.