On 6 May 1097 elements of the crusader army appeared before the city of Nicaea held by Kilij I Arslan, the Seljuk Sultan of Rhüm (1092–1107). The city lies in a fertile basin bounded to the west by the Ascanian Lake (Iznik Gölü). From the south gate (Yenişehir Gate) the land rises sharply into the 800-metre-high Avdan Daglari. From the north gate (Istanbul Gate) the rise into the much higher Naldökan range which the crusaders had crossed is much gentler and only becomes appreciable after three kilometres. To the east (Lefke Gate), a wide and gently sloping valley rises to a watershed then slopes mildly down to the valley of the Sangarius (Sakarya Nehri) and the military roads to Ankara and the Anatolian plateau (see fig. 5). Raymond of Aguilers and Albert of Aachen were much impressed by Nicaea's fortifications which the leaders examined carefully. Fulcher remarked on the determination and cruelty of its garrison. Its fortifications were Roman, dating from the fourth century, but they had been modified and kept in repair under the Byzantine empire. A great wall, pierced at the points of the compass by four main gates, surrounded the city. It was probably about ten metres high and studded with 114 round or square towers rising to seventeen metres, and its circuit measured 4,970 metres. There was a double ditch around the outside.