Asiatic Breezes by Oliver Optic

Captain Ringgold knew something about Aden before he decided to make a stopping-place of it, and it was certainly a more agreeable location than Perim. The town -- or towns, for there appear to be several of them -- is described by a former resident as a sort of crater like that of a volcano, formed by a circular chain of steep hills, the highest of which is 1,775 feet above the sea level. The slope outside of them reaching to the waters of the Arabian Gulf, or the Gulf of Aden as it is now called, has several strings of hills in that direction, with valleys between them, radiating from the group to the shore.

Aden is a peninsula connected with Hadramaut, the southern section of Arabia, by a narrow isthmus, covered at the spring tides by the surrounding waters. Over it is a causeway conveying an aqueduct which is always above the sea level. The region looks as though it might have been subject to volcanic convulsions at some remote period. Within the circle of hills are the town and a portion of the military works. In its natural location, as well as in the strength of its defences, it bears some resemblance to Gibraltar.