Adam Clarke on Obadiah 1:3

The pride of thine heart - St. Jerome observes that all the southern part of Palestine, from Eleutheropolis to Petra and Aialath, was full of caverns hewn out of the rocks, and that the people had subterranean dwellings similar to ovens. Here they are said to dwell in the clefts of the rock, in reference to the caverns above mentioned. In these they conceived themselves to be safe, and thought that no power brought against them could dislodge them from those fastnesses. Some think that by סלע sela, rock, Petra, the capital of Idumea, is intended.