The site of the mound raised before the construction of  an early medieval keeill or chapel which would have been in use between circa AD500 and AD1000.  Cronk yn How was excavated by J.R. Bruce and W. Cubbon in 1928.   


The area bears evidence of occupation from the Neolithic period onwards, but the mound was built in the 7th-8th century for a keeill. Subsequently a stone building, measuring 6 metres by 2.4 metres, was built. It appears to have been an oratory chapel with associate burials of Irish type, tentatively assigned to the 12th century.


It is possible that the mound under the keeill was originally a prehistoric barrow.