The site 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 position of the keeill was shown by the occurrence of lintel graves and cross-slabs. Ten cross-slabs were found (7-8th century). Many were associated with burials, 3 others being incorporated in the later building. 


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 associated burials of Irish type, tentatively assigned to the 12th century. 


Not all the burials in the keeill graveyard were of the lintel type. One belonging to the end of the keeill period had an iron knife and 'button' associated with it. Another, possibly a pagan Scandanavian burial with covering slabs, passed beneath the stone building foundations. There was a horse burial on the west side of the mound, represented by the fragmentary remains, but no dating evidence. Iron nails and rivets apparently associated with the burials were of typical 'Viking' date, as were a green glass bead and fragment of a rune-inscribed standing cross also found at this site. The cross-fragment was found loose in the southeast angle of the building. The remains of the stone building stood centrally on the site, a plain spindle whorl and broken upper stone of a rotary quern were also found.


A large stone, with incised figures of animals, was found in the foundations of the building. P.M.C. Kermode and L'Abbe Breuil compared this with certain Scandanavian rock-engravings. The monument is unique in Britain. The stone was of secondary occurrence but its original site must have been near by. 


The area also bears evidence of occupation from the Neolithic period onwards, but the earliest definite occupation level was tentatively dated to just before to the first Christian church, and contained at least three hearths and an extensive area of scattered charcoal but produced no datable objects.