The early material referring to the Celtic tonsure emphasizes its distinctiveness from the Roman alternative and invariably connects its use to the Celtic dating of Easter. Those preferring the Roman tonsure considered the Celtic custom extremely unorthodox, and associated it with the form of tonsure worn by the heresiarch Simon Magus. This association appears in a 672 letter from Saint Aldhelm to King Geraint of Dumnonia, but it may have been circulating since the Synod of Whitby. The tonsure is also mentioned in a passage, probably of the 7th century but attributed wrongly to Gildas: ""Britones toti mundo contrarii, moribus Romanis inimici, non solum in missa sed in tonsura etiam"" ("Britons are contrary to the whole world, enemies of Roman customs, not only in the Mass but also in regard to the tonsure"). The exact shape of the Irish tonsure is unclear from the early sources, although they agree that the hair was in some way shorn over the head from ear to ear. In 1639 James Ussher suggested a semi-circular shape, rounded in the front and culminating at a line between the ears. This suggestion was accepted by many subsequent writers, but in 1703 Jean Mabillon put forth a new hypothesis, claiming that the entire forehead was shaven back to the ears. Mabillon's version was widely accepted, but contradicts the early sources. In 2003 Daniel McCarthy suggested a triangular shape, with one side between the ears and a vertex towards the front of the head. The "Collectio canonum Hibernensis" cites the authority of Saint Patrick as indicating that the custom originated with the swineherd of Lóegaire mac Néill, the king who opposed Patrick. In Christian Ireland – as well as Pictish and English peoples they Christianised – a distinctive form of penance developed, where confession was made privately to a priest, under the seal of secrecy, and where penance was given privately and ordinarily performed privately as well. Certain handbooks were made, called "penitentials", designed as a guide for confessors and as a means of regularising the penance given for each particular sin. In antiquity, penance had been a public ritual. Penitents were divided into a separate part of the church during liturgical worship, and they came to Mass wearing sackcloth and ashes in a process known as "exomologesis" that often involved some form of general confession.