unified and formed a centralised kingdom known as Strathclyde. None of the documentary or archaeological evidence from the period when the Roman legions arrived suggests that battles took place in the area. Therefore the Roman legions and Damnonii tribespeople are assumed to have been on good terms and to have co-operated by means of trade and the exchange of military information. The Romans did, however, construct several forts () in the area, notably on the banks of the Clyde. These include Castledykes, Bothwellhaugh, and Old Kilpatrick and Bishopton. The Romans also constructed several roads along the river, both small ones and larger ones designed to be used as trade routes and to carry entire legions. The Antonine Wall, which lies only a few miles from the river, was constructed later by the Romans as a means of defending the area against invasion by the Picts. Despite the strategic location and flat terrain of Glasgow and the surrounding Clyde basin, no Roman civilian settlement was ever constructed. Instead, the region mostly functioned as a frontier zone between the Roman province known as Britannia Inferior and the Caledonians, an indigenous group that was hostile to the Romans. Kingdom of Strathclyde Strathclyde was founded as an independent British kingdom, either during or shortly after the Roman occupation of Britain. The kingdom's core territory and much of its arable land was located around the Clyde basin. The kingdom was ruled from its capital, the near impenetrable Alt Clut fortress (Dumbarton Rock), which was situated on the river and overlooked much of the estuary. This fortress was noteworthy enough to have been referred to at the time in several letters and poems about Sub-Roman Britain, written by Gildas and others. Strathclyde remained a powerful kingdom during the early medieval period in Britain. It was also a reservoir of native Welsh culture: Its territory eventually expanded along the Clyde Valley, through the Southern Uplands and Ayrshire, and southward into Cumbria. In the 7th century, Saint Mungo established a new Christian community on the banks of the Clyde, replacing Cathures. This community was the beginnings of what would become the city of Glasgow. Several villages on the Clyde that were founded then have endured to this day, and grown to become towns, including Llanerc (Lanark), Cadzow (Hamilton), and Rhynfrwd (Renfrew). The fortress of Altclut fell in the Siege of Dumbarton of 870 AD, when a force of