The other towns depend for the most part on their position on lines of communication between or from these three cities. But the exact siting has depended chiefly on three factors, first the possi bility of markets, which has depended largely on positions along the rivers, and especiajly at the confluence of two rivers or canals, secondly a central position in a specially favourable district and thirdly, religious sanctity which has attached itself to a particular locality. Of these pilgrim centres the most important are Kerbela and Nejef, to which towns Shiah Muslims come from all over Mesopotamia and Persia and wherever else members of that faith are to be found. At Nejef there is the tomb of Ali, the finest of the Shiah monuments ; it is also a starting point for one of the regular roads to Mecca, via the Wadi Jowf. Both these towns lie on the western boundary of Mesopotamia. Samarra on the Tigris, north of Baghdad, is a pilgrim centre of lesser importance.
The Euphrates towns group themselves first into those on the caravan route between Baghdad and Aleppo. This group which includes Birijik, Urfa, Diarbekr, Mardin, Nisibin and Jezireh-ibn Omar have avoided the open plains and the southern end of the Karaja Dagh as being too insecure and waterless. Below Birijik on the middle Euphrates there are a series of towns of great est importance. Rakka, the ancient Nicephorum, at the junction of the Belik and Euphrates lies somewhat off the road but Deir-ez Zor near the junction of the Khabur and the main stream is of the greatest importance, because the regions both to the east and west are less arid than the corresponding regions lower down the river and are therefore more readily traversed by caravans. Fur ther south along the river lie \Verdi, Ana, Hit and Ramadi. All these towns, including Deir-ez-Zor lie on the western bank. At Ramadi there is a bridge of boats and the place is of some impor tance to-day as it forms the starting point of the overland motor route to Jerusalem. It is also an Air Force station, for apart from the Rutba wells out in the desert there is no other permanent water available till Amman is reached. A newer town is growing up on the other bank of the river. On the lower Euphrates apart from the pilgrim centres already mentioned there are a series of towns of growing importance owing to the presence of the railway. These are Hilla, close to the site of ancient Babylon, a great grain market, built on both sides of the river, the two parts of the town being connected with a bridge of boats. Hilla possesses large bazaars.
It is of great interest as being a town which preserves, without any of the special prohibitions which attach to religious centres, the appearance of a truly oriental town little influenced by western culture. Lower on the river are Diwaniyeh, Nazariyeh and Suk esh-Shiyukh, while Kurna lies at the junction of the twin rivers. There are few towns on the Tigris. Apart from Baghdad and Mosul the most important are Tekrit, with raft traffic downstream to Baghdad, an ancient industry in the time of Herodotus, and Kut-el-Amara and Kut. There are however a series of towns on the eastern frontier. Rowanduz in south Kurdistan is on the cara van route from Mosul to Tabriz, while Suleimaniye is the great market centre, being connected both with Mosul and Baghdad, and lies on the caravan route between this town and northern Persia. On the actual edge of the hills lie the towns of Erbil, Altun Kipri, Kirkuk, Tuz Khurmantli and Salahiye.