The centre of Aarhus was once a pagan burial site until Aarhus' first church, Holy Trinity Church, a timber structure, was built upon it during the reign of Frode, King of Jutland, around 900.In the 900s an earth rampart for the defence of the early city was also constructed, encircling the settlement, much like the defence structures found at ring fortresses elsewhere. The rampart was reinforced later on by Harald Bluetooth, and together with the town's geographical placement, this suggests that Aros was an important trade and military center. There are strong indications of a former royal residence from the Viking Age in Viby, a few kilometres south of the Aarhus city centre.The bishopric of Aarhus dates back to at least 948, when written sources mention the bishop of Reginbrand attending the synod of Ingelheim in Germany. The bishopric and the town's geographical location propelled prosperous growth and development of the early medieval town.The finding of six runestones in and around Aarhus indicates the city had some significance around the year 1000, as only wealthy nobles traditionally used them.