<P> The Celtic cross is a form of Christian cross featuring a nimbus or ring that emerged in Ireland and Britain in the Early Middle Ages . A type of ringed cross, it became widespread through its use in the stone high crosses erected across the islands, especially in regions evangelized by Irish missionaries, from the 9th through the 12th centuries . </P> <P> A staple of Insular art, the Celtic cross is essentially a Latin cross with a nimbus surrounding the intersection of the arms and stem . Scholars have debated its exact origins, but it is related to earlier crosses featuring rings . The form gained new popularity during the Celtic Revival of the 19th century; the name "Celtic cross" is a convention dating from that time . The shape, usually decorated with interlace and other motifs from Insular art, became popular for funerary monuments and other uses, and has remained so, spreading well beyond Ireland . </P> <P> Ringed crosses similar to older Continental forms appeared in Ireland and Scotland in incised stone slab artwork and artifacts like the Ardagh chalice . However, the shape achieved its greatest popularity by its use in the monumental stone high crosses, a distinctive and widespread form of Insular art . These monuments, which first appeared in the 9th century, usually (though not always) take the form of a ringed cross on a stepped or pyramidal base . The form has obvious structural advantages, reducing the length of unsupported side arms . There are a number of theories as to its origin in Ireland and Britain . Some scholars consider the ring a holdover from earlier wooden crosses, which may have required struts to support the crossarm . Others have seen it as deriving from indigenous Bronze Age art featuring a wheel or disc around a head, or from early Coptic crosses based on the ankh . However, Michael W. Herren, Shirley Ann Brown, and others believe it originates in earlier ringed crosses in Christian art . Crosses with a ring representing the celestial sphere developed from the writings of the Church Fathers . The "cosmological cross" is an important motif in Coelius Sedulius's poem Carmen Paschale, known in Ireland by the 7th century . </P> <P> It is not clear where the first high crosses originated . The first examples date to about the 9th century and occur in two groups: at Ahenny in Ireland, and at Iona, an Irish monastery off the Scottish coast . The Ahenny group is generally earlier . However, it is possible that St. Johns Cross at Iona was the first high cross; Iona's influence as a center of pilgrimage may have led this cross to inspire the Ahenny group as well as other ringed crosses in Pictish stones . </P>

What does the circle in a celtic cross represent
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