The kingdom ruled by Kenneth's descendants—older works used the name House of Alpin to describe them but descent from Kenneth was the defining factor, Irish sources referring to Clann Cináeda meic Ailpín (the Clan of Kenneth MacAlpin)—lay to the south of the previously dominant kingdom of Fortriu, centred in the lands around the River Tay. The extent of Kenneth's nameless kingdom is uncertain, but it certainly extended from the Firth of Forth in the south to the Mounth in the north. Whether it extended beyond the mountainous spine of north Britain—Druim Alban—is unclear. The core of the kingdom was similar to the old counties of Mearns, Forfar, Perth, Fife, and Kinross. Among the chief ecclesiastical centres named in the records are Dunkeld, probably seat of the bishop of the kingdom, and Cell Rígmonaid (modern St Andrews).