My study has explored (a) the origins of the high cross in Ireland and (b) the developments of the Celtic high cross over the past 1400 years. The origins can be traced to Constantine in AD 312. Developments relate to interpretations of the Constantine story, involving the "IHS" insignia and other elements such as the "radial" display. The form of the ringed cross became very important, and it was carved onto the surface of gravestones as a symbol. Another retention of form can be seen in the "boss" element, which serves as an aesthetic reminder rather than as a utilitarian structure.
Spatially (or geographically), the gravestones in Ireland are remarkably similar. The gravestones of Irish immigrants in California, though, are found to be much different from their Irish counterparts, and they are also found to show more variation amongst themselves. Apparently, the traditional mortuary art motifs lost some of their value for the Irish immigrants.
Among other things, my study has shown the value of studying mortuary artworks as archaeological material. Gravestones relate a wealth of cultural information. They are subject to the same temporal and spatial variation as other artifacts (like pottery and stone tools). Furthermore, gravestones are associated with ideological concepts of death, and these concepts are very important for our understanding of cultures both past and present.