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The Roman conquest of Britain began in 43 AD but advance beyond the Humber did not take place until the early 70s AD. This was because the people in the area known as the Brigantes by the Romans became a Roman client state. When their leadership changed becoming more hostile to Rome Roman General Quintus Petillius Cerialis led the Ninth Legion north from Lincoln across the Humber.[1]. Eboracum was founded in 71 AD when Cerialis and the Ninth Legion constructed a military fortress (castra) on flat ground above the River Ouse near its junction with the River Foss. In the same year Cerialis was appointed Governor of Britain.[2]
A legion at full strength at that time numbered some 5,500 men, and provided new trading opportunities for enterprising local people, who doubtless flocked to Eboracum to take advantage of them. As a result permanent civilian settlement grew up around the fortress especially on its south-east side. Civilians also settled on the opposite side of the Ouse, initially along the main road from Eboracum to the south-west. By the later 2nd century, growth was rapid; streets were laid out, public buildings were erected and private houses spread out over terraces on the steep slopes above the river.
From its foundation the Roman fort of Eboracum covered an area of 50&_160;acres (0.202&_160;km²) the standard size for a legionary fortress. The layout of the fortress also followed the standard for a legionary fortress with wooden buildings inside a square defensive boundary.[3] These defences originally consisting of turf ramparts on a green wood foundation, were built by the Ninth Legion between 71 and 74 AD. Later these were replaced by a clay mound with a turf front on a new oak foundation, and eventually, wooden battlements were added which were then replaced by limestone walls and towers.[4] The original wooden camp was refurbished by Agricola in 81, before being completely rebuilt in stone between 107 and 108.
