According to tradition, they cover the remains of two standard-bearers of the Prophet. Hard by is a fine vaulted well; and the group are the sole exceptions to the tale of ruin told by the heaps of crumbling bricks which stretch as far as the eye can see. The oldest of the ruined cities of the plain, called Giaur Kal`a, stood eastwards of these monuments. It was destroyed in the seventh century, when the Caliph `Omar’s lieutenants carried their creed through Central Asia by fire and sword. Giaur Kal`a is identified by its vast earthen ramparts, which have proved more durable than the bricks and mortar of a much later age. As in the case with Bahrām `Alī, there are the remains of a citadel at its north-eastern angle, from which an extended view can be had of the poor relics of vanished splendour. North-west of Giaur Kal`a are the only buildings of ancient Merv which continue to serve the purposes of man. They are a serai and mosque, which have clustered round the ugly tomb of a saint named Yūsuf Hamadāni. It contains the usual vaulted chambers for the accommodation of travellers, ranged in a square in which their goods and camels find standing room. Beyond it is the tomb of Sultan Sanjar, exactly in the centre of the site of the second of the towns which successively bore the name of Merv. It is said to have been modelled on that of Firdawsi near Meshed, but it closely resembles the great mausolea of Upper India. All are alike, quadrangular buildings topped with an echoing dome, which gives a sense of vastness and solemnity beyond anything that the “long-drawn aisle and fretted vault” can compass. Even in its ruin the splendid edifice shows feats of workmanship in brick and mortar which it would be difficult to imitate with all the appliances of modern science. The Sultan who sleeps below was the best of the Seljūk Turks; and, to judge from the abundance of offerings piled on the rude clay mound which covers his remains, he still lives in the hearts of the people. The noble work was seen in all its majesty by only two generations; for in 1221 the city of the good Sultan Sanjar was razed to the ground, with a fearful slaughter of the inhabitants, by Tulūy Khān, a worthy son of the ferocious Chingiz. Here the ground is strewn with fragments of pottery exhibiting strangely beautiful designs, iridescent glass and enamelled tiles; and no one can doubt that systematic researches would yield more substantial tokens of a buried civilisation. The source of the fabulous wealth of Old Merv stands revealed in the numerous irrigating channels with which the site is scored. This is the land where-- “----fairest of all streams, the Murga roves, Amongst Merou’s bright palaces and groves.”[683]