=The Arnon.= Farther south the Arnon, the chief river of Moab, rises on the border of the desert. Rapidly cutting its way down into the plateau, it receives its first important confluent from the south, and farther on the Wady Waleh from the north. At the point where the central highway through Moab from the north crosses the Arnon the canyon is three thousand feet deep and two miles from bank to bank. It is by far the most stupendous and picturesque chasm in all Palestine.^{(48)} The steep red cliffs, variegated and richly colored by white, gray, and yellow strata, extend in wavy billows east and west as far as the eyes can reach. The descent is almost sheer into the depths below, where the river, easily fordable at many points and with an actual channel only a few feet wide, rushes over the smooth rocks or winds leisurely through its fringe of oleanders and green bushes. Where the tributary wadies have cut down the soft limestone, nature's castles stand out, guarding the broad natural highway from the desert to the sea. The Arnon only in a lesser degree separated the land of Moab and destroyed its political unity, even as did the Jordan the land of Israel. =Southern Moab and Edom.= Farther south the Wady el-Kerak, narrow and deep, runs past both sides of the natural citadel, whose name it bears,^{(49)} and finds its way to the Dead Sea back of the barren promontory of El-Lisan. Thus the three zones of Moab, the western promontories, the central fields, and the dry pasture lands on the east, are repeatedly intersected by the deep gorges that make it a land easy to approach from the desert and difficult to defend. Farther south the plateau of Moab merges into the wild, picturesque mountains of Mount Seir, the home of the Edomites. The valley becomes narrower and the mountains bolder, more jagged, and abrupt. The culmination of these natural wonders is the Wady Mûsa, which cuts a deep, narrow channel through the heart of the mountains.^{(50)} In the midst of this valley, surrounded by gorgeously colored sandstone cliffs, out of which have been carved homes, streets, tombs, theatres, temples,^{(51)} and well-preserved high places,^{(52, 53)} stands that most astonishing and marvellous of all oriental cities--Petra.