Long after the time of the primitive mythology, the more striking features of the land continued to appeal to the Hellenic imagination and to perpetuate the prowess of gods and heroes, even down to generations of men among whom belief in these legends was already beginning to grow dim. The narrow gorge of Tempe may be cited in illustration of this influence. Cleft between the precipices of Olympus and Ossa, and serving as the only outlet for the drainage of the wide Thessalian plain, this chasm must have arrested the attention of the earliest settlers, and certainly continued for many centuries to be one of the most noted valleys of the Old World. The contrast between the vast level plain through which the River Peneius and its tributaries wander, and the narrow gorge through which the accumulated waters issue; the apparently insurmountable barrier interposed across the course of the stream; the singular and unexpected ravine by which the drainage is allowed to escape to the sea; the naked, fissured walls of white limestone on either side of the narrow pass, even now powerfully impress the observant traveller of to-day. These striking features could not fail to appeal to the imagination of the old Greek. From early times it was recognised that the plain of Thessaly had once been covered with a sheet of water, of which the remaining portions formed two considerable lakes. Had no passage been opened for the outflow of the drainage across the barrier of mountains the plain would have remained submerged. The cleaving of a chasm whereby the pent-up waters were allowed to flow down to the sea, and thus to lay bare so wide an area of rich land for human occupation, was looked on as the work of some benevolent power, and naturally came to be associated with the name of Poseidon, the God of the Sea.[8] In later times, when the deeds of gods and heroes began to be confounded with each other, the supernatural character of the Vale of Tempe was still acknowledged; but the opening of the cleft was in course of time transferred to Hercules, who, by cutting a hollow across the ridge, allowed the stagnant waters of the interior to flow off into the sea.[9]