The city of Albi is built on the steep banks of the Tarn, which drains the high table-land sloping gradually from the Cevennes to the vast plain of Languedoc. From whichever side the city be approached the lofty and massive structure of the cathedral church is seen dominating the surrounding buildings. The church, with the adjoining episcopal fortress, crowns the cliff on the left bank of the river. Adjacent to the west end of the church, and occupying the extreme point of the cliff, is the site of Castel-viel, now represented by a group of humble dwellings. Here was once a Gaulish oppidum, and later a Roman fort was erected to protect the ferry over the Tarn, which divided the territory of the Ruteni. This bourg was defended by an important fort belonging to the viscounts of Albi, who held it from their over-lords, the counts of Toulouse, and it was isolated on three sides by the ravines through which the Tarn and its tributary stream the Verdusse run, and on the east side by a moat dividing it from Albi.