The triads give some indication of the naval powers at the time. Triad 14 mentions the Seafarers/Fleet Owners. Geraint ab Erbin and March ap Meirchion were both of Cernyw. There must have been frequent communication between this kingdom and those of Brittany for the LL to regard them as “one people and one language”. Triad 15 gives the Roving Fleets and Bromwich suggests the names may indicate they were Irish while those of the previous triad were British. It may be that with Tintagel being on the north coast, the Cornish and Irish together controlled all trade going through the Irish Sea. Likewise Dumnonia and Brittany could have dominated commerce through the English Channel.
 Bromwich, R., 2006, 30