Coldingham may seem like an odd choice for a fortress britain post, but it did start out as a fortress. Archaeological investigation of the monastery of Coldingham showed a 6th century British fortress on the site. It has the typical double pallisade found in Gododdin and Bernician territory.
We really don’t know anything about the site as a fortress. The name Coludaesburg means ‘fortress of Coludae’, a British name. Fraser notes that there is a dynast named Coledauc was the son of Morcant, usually associated with Gododdin and with the instigator of the assassination of Urien Rheged. It would made perfect sense for Morcant of Gododdin to be involved in a siege of Medcaut/Lindisfarne. Interestingly Morcant’s instigation of Urien’s assasination actually supported Bernician survival, not as surprising as it may seem considering the early Bernicians may have been originally employeed by Gododdin. Morcant’s son Coledauc would also be the right age to be the last British ruler at Coldingham when it came under Bernician control.
Fraser suggests that Coledauc may have “donated” it to be a Bernician royal convent. I think its more likely that he was the last owner of Coldingham before the Bernicians gave it to Oswiu’s sister Æbbe. His name could remain associated with the site either way. Many sites in Bernicia/Gododdin retained their British name. A British donation suggests that the British retained some control in the immediate area, and I don’t think that the Bernicians would have trusted their royal women to an area where there was still some local British control. I also think that Coldingham didn’t come into being until the time of Oswiu, and I think its unlikely that Coledauc would have retained control of a fortress for that long. Even so, he still could have been the last ruler and/or possible builder of the fortress.
James Fraser. From Caledonia to Pictland: Scotland to 795. Edinburgh University Press, 2009 at p. 169-170.