High Crosses of Ireland - they are the source of much confusion. As many a tourist will tell you:
"You should have seen all those crosses, you know, the Celtic ones ... the High Crosses ... in every cemetery!" Ah, we have spotted the usual confusion. Irish memorial crosses, Celtic crosses and High Crosses seen as synonymous - which they are not. The High Cross, as "typically Irish" as the (often nearby) round tower in many eyes, can be quite clearly defined - which does not prevent hundreds of other crosses being labelled in this way.
The Celtic Cross - an Irish Original?
When one mentions a Celtic cross, this automatically summons up the image of a Latin (conventional) cross with the stem and arms linked by a circular addition. This specific form of the main Christian symbol may have had its origin in Ireland, though it is also known in Cornwall, Wales, Northern England and parts of Scotland - all areas being in contact with Ireland during the so-called "Dark Ages". So maybe this cross, now regarded as something of a Pan-Celtic symbol, came with Irish missionaries.
Whatever the historical background of its origin - the historical development of the unusual cross is even less clear. Unless you subscribe to the outlandish idea that some Irish clerics deliberately chose a "trademark" and consciously designed the Celtic cross.
How the ring became part of the cross is totally unclear. And open to interpretation - some scholars went as far as to suggest that the ring represents a halo and thus Christ himself, circumventing any scruples about picturing God's son. These theories are close cousins to those that suggest that the circle should really be a disk, representing sol invictus, the sun-god.
Personally I would stick with Occam's razor and the very pedestrian theory that the ring was introduced by the masons. Not the Freemasons, mind you, but simple craftsmen wanting to add a bit of stability to the construction. So maybe there is no symbolism hidden here at all?
But the Celtic cross has certainly acquired a new symbolism in recent years - white supremacists have appropriated the cross as an alternative to the swastika!
Why were High Crosses Erected?
For one reason only - to mark a sacred space and to declare adherence to the Christian beliefs. Basically a sign saying "Here be Christians!", but also "This is hallowed ground, keep its peace!"
Apart from this the crosses were also a focal point of celebrations - out of necessity one might say. The classic layout of the early monastic settlements included a church, a cross and (if funds permitted) a round tower - the latter's door oriented towards the first's entrance, with the cross in the middle. And the church was usually too small for even a modest congregation. Which meant that the huddled masses had to attend mass al fresco. Gathered around the cross.
But not all High Crosses were of an ecclesiastical nature - some seem to have been connected to territorial rights, marking a market place for instance. Others were erected to commemorate an important event or person.
The only use High Crosses were not put to was ... as an actual grave marker.
The Early Evolution of High Crosses
No historian can tell us where, when or even why the first High Crosses were erected. But it is assumed that the first stone crosses were "copies" of wooden crosses covered with metal. Several (necessary) features of these earlier crosses were incorporated into the design.
Some crosses of this type are from the 8th and 9th century, like the northern cross at Ahenny, covered in geometrical designs. The most important feature was the basic form of the cross itself. Not necessarily as the representation of an instrument of execution but as an image of the early chi rho monogram.