Dumovaria was founded about 70 AD, as part of the Roman policy of civilising the Britons by helping them to build tribal capitals in Roman style, and it was peopled at ﬁrst by a migration from the old town at Maiden Castle. Originally it had no defences, but about sixty years later it was surrounded with a wide ditch and earth bank. About 200 AD, as in other towns, the earth rampart was faced with a stone wall.
The space of some eighty acres within the Wall has been so thickly inhabited since Roman times that only deep excavation reaches the Roman layer and nothing is so far known of the public buildings — Baths, Forum, temples, and inn — which Roman Dorchester must have had. A few separate houses have come to light, mosaic ﬂoors from which have been relaid in the Dorchester Museum, and the remains of the one on the County Hall site in Colliton Park may still be seen. Little is known of the street plan, but the present High Street runs almost on the line of the main Roman road through the town.
Water for the baths, and perhaps also for domestic use, was brought by a remarkable open-channel aqueduct several miles long which left the River Frome below Frampton and may still be traced along the hillside. It probably passed under the ditch and Wall by a siphon, and it entered the town at a height from which water could be distributed by gravity on the same principle as the modern water—tower. No burials were allowed inside Roman towns, and consequently the cemeteries discovered are all beyond the Wall, especially near the East Gate.
The Roman surveyors chose the site for the new capital so well that in Saxon times it again became the county town and has remained so ever since.