The Roman and, consequently, the Saxon conception of episcopal government was territorial and diocesan; the Celtic conception was tribal and monastic. An ecclesiastical system based upon tribal and monastic principles, recognising no supreme central authority, can afford to dispense with clearly defined boundaries. At the same time a monastic, no less than a tribal organisation, requires a centre of its own, towards which its activities may converge, and from which its influences may radiate. The present is an attempt to show where the more important of such centres existed in Cornwall before diocesan was substituted for monastic rule. Doubtless every _lan_ represented some such centre, however insignificant, just as every _caer_ represented a fortified seat of civil authority. The _lan_ justified its existence by the strength and fervour of its prayers and spiritual influence: the _caer_ by the strength of its natural position and its artificial defences. A monastic settlement with a definite amount of demesne land, corresponding to its size and importance, upon which the monks worked for the support of the community, will sufficiently indicate what is meant. Some monasteries had bishops; some—the greater number—were without them. The great monasteries of Landévennec in Brittany, Llantwit in Wales, and Bangor in Ireland, do not appear to have had bishops of their own, or, if they had, their episcopal character was submerged. On the other hand, the monastery-bishoprics of all three countries are too well known to require demonstration. The isolation of the Church in Cornwall until the middle of the tenth century encouraged and perpetuated the system in the mother country which in the fifth and sixth century it had helped to establish in Brittany. Domesday Book, when studied by the light of earlier and later records, supplies invaluable information upon the subject of Cornish ecclesiastical organisation even before the Saxon conquest. At the time of the Great Survey (1086), the bishop of Exeter held the following manors in Cornwall: Treliuel (Treluswell in St. Gluvias). Matela (Methleigh in St. Breage). Tregel (Trewell in St. Feock). Pauton (Pawton in St. Breock). Berner (Burneir in Egloshayle). St. German (St. Germans). Lanherneu (Lanherne in Pydar). Tinten (Tinten in St. Tudy). Languititon (Lawhitton). Landicla (Gulval). St. Winnuc (St. Winnow).