The country on which they had now entered was, in some of its features, familiar to the invading army, but in others new and strange. From the head of the Persian Gulf to the Dead Sea there stretches right across the peninsula a stony wilderness, trackless and waterless. As you advance north, nature relaxes its severity; the plain, still a desert, is at certain seasons clothed with verdure, bright with flowers and instinct with the song of birds and hum of insect life. Such is the pasture-land which for several hundred miles extends from Damascus to the Tigris. Still further north, the desert features gradually disappear, and, about the latitude of Mosul, are blended with the hills and fields of Asia Minor. Athwart this vast plain, from Aleppo to Babylon, runs the river Euphrates, and the far east is bounded by the Tigris flowing under the mountain ranges of Persia. Between the two rivers lies the _Jezîra_, or ‘Island,’ of Mesopotamia, full of patriarchal memories. Over this great waste there roamed (as still roam) Bedouin tribes with their flocks and herds. The greater part of these Arabs had for centuries professed the Christian religion. Those on the Syrian side, as the Beni Ghassân of Bostra, owed allegiance to the Roman Empire; while on the east, like the Lakhmites of Hîra, they were dependent upon Persia.[100] But nomad life tends to fickleness of attachment and laxity of faith; and, not infrequently, affinity with their brethren of Arabia, and the lust of plunder, led these northern Arabs, deserting now their ancient allies and their ancestral faith, to cast in their lot with the invading columns. [Sidenote: Chaldæa and the delta of the Euphrates. Irâc Araby.]