A Celtic cross combines the cross with a ring surrounding the intersection. It is the characteristic symbol of Celtic Christianity, though it may have older, pre-Christian origins. Such crosses formed a major part of Celtic art.
In Celtic regions of Ireland and Britain many free-standing upright crosses – or high crosses – were erected, beginning at least as early as the 7th Century. Some of these 'Celtic' crosses bear inscriptions in runes. There are surviving free-standing crosses in Cornwall and Wales, in the island of Iona and in the Hebrides, as well as the many in Ireland. Other stone crosses are found in Cumbria and the Scottish Borders, however some of these are of the Anglo-Saxon cross making tradition. The most famous standing crosses are the Cross of Kells, County Meath, and the crosses at Monasterboice, County Louth, Ireland, and the Cross of the Scriptures, Clonmacnoise, Ireland
There are numerous representation of crosses combined with a circle, even before Christianity. Often called "sun cross", they can be found in pagan North-West Europe (the symbol became the mark of the Norse god Odin) or in Pyrenees and in Hiberica Peninsula. But there is no evidence of a link or a common origin with the Christian cross.
It should be noted that the Old English word for "cross" is "rood". The word "cross" in English derives only indirectly from Latin crux, crucis, passing through the intermediary of Old Norse kross. Linguistically it is striking that the pagan Norse raiders ("Vikings") should have impressed their word for "cross" on the Christianized Anglo-Saxons.
In Ireland, it is a popular myth that the celtic cross was introduced to the island by Saint Patrick during his time converting the pagan Irish. It is believed that he combined the symbol of christianity, a cross, with the symbol of the sun, to give pagan followers an idea of the importance of the cross by linking it with the idea of a pagan sun-god.
Celtic crosses have been the dominant image of the wide variety of celtic art used in tattoos. Popular through the world, with heavy concentration in the United States and Ireland, bearers of celtic cross tattoos are often Irish or Irish diaspora exercising cultural identification. Although, many others choose a celtic cross tattoo simply because they enjoy the unique ornamental style of celtic art.