Xerxes reduced the ancient city almost to a heap of ashes. After the departure of the Persians, its reconstruction on a much larger scale was commenced under the superintendence of Themistocles, whose first care was to provide for its safety by the erection of walls. The Acropolis now formed the centre of the city, round which the new walls described an irregular circle of about 60 stadia or 7 1/2 miles in circumference. The space thus enclosed formed the ASTY, or city, properly so called. But the views of Themistocles were not confined to the mere defence of Athens: he contemplated making her a great naval power, and for this purpose adequate docks and arsenals were required. Previously the Athenians had used as their only harbour the open roadstead of PHALERUM on the eastern side of the Phaleric bay, where the sea-shore is nearest to Athens. But Themistocles transferred the naval station of the Athenians to the peninsula of Piraeus, which is distant about 4 1/2 miles from Athens, and contains three natural harbours,--a large one on the western side, called simply Piraeus or The Harbour, and two smaller ones an the eastern side, called respectively ZEA and MUNYCHIA, the latter being nearest to the city. It was not till the administration of Pericles that the walls were built which connected Athens with her ports. These were at first the outer or northern Long Wall, which ran from Athens to Piraeus, and the Phaleric wall connecting the city with Phalerum. These were commenced in B.C. 457, and finished in the following year. It was soon found, however, that the space thus enclosed was too vast to be easily defended; and as the port of Phalerum was small and insignificant in comparison with the Piraeus, and soon ceased to be used by the Athenian ships of war, its wall was abandoned and probably allowed to fall into decay. Its place was supplied by another Long wall, which was built parallel to the first at a distance of only 550 feet, thus rendering both capable of being defended by the same body of men. Their height in all probability was not less than 60 feet. In process of time the space between the two Long Walls was occupied on each side by houses. It will be seen from the preceding description that Athens, in its larger acceptation, and including its port, consisted of two circular cities, the Asty and Piraeus, each of about 7 1/2 miles in circumference, and joined together by a broad street of between four and five miles long.