Although Alexander had landed safely on the Asiatic shore, the way was not yet fairly open for him to advance into the interior of the country. He was upon a sort of plain, which was separated from the territory beyond by natural barriers. On the south was the range of lofty land called Mount Ida. From the northeastern slopes of this mountain there descended a stream which flowed north into the sea, thus hemming Alexander's army in. He must either scale the mountain or cross the river before he could penetrate into the interior.