Virtual reconstruction of Hammaburg in Ansgar's time (before 845). View from the southeast. View over Hammaburg, Ansgar's church and the settlement close to the river Alster. Before Ansgar's arrival, Hammaburg was already a significant border town and place of trade. As a mission base for the whole north, it became the centre of Nordalbingia. In Ansger's time, Hammaburg had a castle, a church, settlements in the rural area and a harbour area with port and market.