About Dating the Medieval Churches of Gotland By Heikki Ranta, Joakim Hansson, Alf Lindroos, Åsa Ringbom, Jan Heinemeier, Fiona Brock & Gregory HodginsIn 2006 the project »Mortar dating of the Gotland churches« was initiated, with the aim to test how mortar dating would work in a geological area so dominated by Silurian limestone, and how the results of this method could affect the prevailing chronology of the churches. Initial testing was done on three different churches, the church of Bro in the northern part of the island, and with Hamra and Vamlingbo in the south. The result is that mortar based on Silurian limestone behaves much the same way as mortar including Åland Ordovician limestone. Thus, based on mortar dating a chronology of the church of Bro can be seen as follows: A Romanesque nave from ca AD 1040-1160, with an almost contemporary tower in the west, with an additional chancel in the east from the 13th century. In the church of Hamra, the lower part of the west tower, and possibly also the earlier part of a cruciform plan, dates from 1165-1220. Later, in 1260-80, the tower was heightened. The chancel in the east is an addition from the 14th century. In Vamlingbo, the focus was on a secondary support construction of disputed age, built against a south portal. This time the mortar was contaminated by unburned limestone, and the result of mortar dating remains inconclusive. However, fragments of wood and charcoal, incapsuled in the mortar, suggest a terminus post quem some time in the 14th century. It is most likely that the supporting wall is a medieval construction. At this initial stage it seems that the results of mortar dating in turn support earlier prevailing views on the chronology. The results also coincide with occasional dendrochronological dates and with contemporary inscriptions in the churches. It seems that mortar dating can be a helpful tool in forming an objective base for a chronology of the Gotland churches.