The Acropolis was also a sort of fortress, because it was an eminence, and its sides of craggy rock allowed of but one ascent; thus it could be easily defended. Then, when all the wonders and riches of art had been collected there, the pure white marble, the sculpture and painting, and the ornaments of shining metals which glistened in the sun, while brilliant colors added their rich effect, it might be called a gorgeous museum, such as has never since been equalled in the history of the world. It is important to know that the Athenians worshipped three different goddesses, all called by the one name of Athene or Athena. The most ancient and most sacred of these was Athena Polias, whose statue, made of olive-wood, was believed to have fallen from heaven. The Erechtheium was dedicated to this goddess, and there this holy, heaven-sent figure was kept, with other sacred objects of which I shall speak in their place. The Athena next in importance was the goddess of the Parthenon, or the "House of the Virgin," as the word signifies, for this Athena Parthenos is the same as the goddess Minerva, who is said never to have married or known the sentiment of love; she was the goddess of war, prudence, and wisdom. The third Athena was called Promachos, which means the champion. Phidias made of her one of his splendid statues, standing erect, with helmet, spear, and shield. In describing the Acropolis we shall begin with the Propylæa, or the entrances, which occupy the centre of our picture and to which the steps lead, showing the passage between the pillars, three being left on each side. This magnificent series of entrances--as the whole ascent from the outer gate in the wall, up the steps, and through the passage between the pillars may be called--was erected about 437 B.C., and cost two thousand talents of gold, which is equal to about two millions of our dollars. The fame of the Propylæa was world-wide, and together with the Parthenon it was considered the architectural glory of the Periclean age. The style in which they are built is a splendid example of the combination of the Doric and the Ionic orders, for while the exterior is almost pure Doric, the interior is made more cheerful by the use of the Ionic columns and ornamentation. High up at the right of the picture stands the Parthenon. Its architecture, which is Doric, has been described. We do not know when this temple was begun, but it is probably on the site of an older one. It was finished 438 B.C., and the general care of its erection was given to Phidias, the most famous of all sculptors. The marble of which the Parthenon was built was pure Pentelic, and as it rested on a rude basement of limestone the contrast between the two made the marble of the temple seem all the finer. Within and without this temple abounded in magnificent sculptures executed by Phidias himself or under his orders.