The date of first construction of a church in Llangaffo ( a village in Anglesey about 5 miles ( 8 @.@ 0 km ) south of the county town of Llangefni ) is uncertain . The village take its name from the church : the Welsh word llan originally meant " enclosure " and then " church " , and " -gaffo " is a modified form of the saint 's name . St Caffo , a 6th @-@ century Christian , was a companion of St Cybi and was martyred by shepherds in the vicinity of what is now Llangaffo , perhaps in revenge for his brother Gildas insulting Maelgwn Gwynedd , the local ruler . It is thought that there may have at one point been a monastery in this location , known as " Merthyr Caffo " : merthyr is the Welsh word for " martyr " , and in place names mean a building erected near a saint 's grave .