The house--a slight, one-storied building on a space of rocky platform--looks down upon a sandy hollow which now presents much the same appearance that it must have presented when Mariette was first reminded of the fortunate passage in Strabo. One or two heads of sphinxes peep up here and there in a ghastly way above the sand and mark the line of the great avenue. The upper half of a boy riding on a peacock, apparently of rude execution, is also visible. The rest is already as completely overwhelmed as if it had never been uncovered. One can scarcely believe that only twenty years ago the whole place was entirely cleared at so vast an expenditure of time and labor. The work, as I have already mentioned, took four years to complete. This avenue alone was six hundred feet in length and bordered by an army of sphinxes, one hundred and forty-one of which were found _in situ_. As the excavation neared the end of the avenue, the causeway, which followed a gradual descent between massive walls, lay seventy feet below the surface. The labor was immense and the difficulties were innumerable. The ground had to be contested inch by inch. “In certain places,” says Mariette, “the sand was fluid, so to speak, and baffled us like water continually driven back and seeking to regain its level.”[12] If, however, the toil was great, so also was the reward. A main avenue terminated by a semicircular platform, around which stood statues of famous Greek philosophers and poets; a second avenue at right angles to the first; the remains of the great temple of the Serapeum; three smaller temples; and three distinct groups of Apis catacombs were brought to light. A descending passage opening from a chamber in the great temple led to the catacombs--vast labyrinths of vaults and passages hewn out of the solid rock on which the temples were built. These three groups of excavations represent three epochs of Egyptian history. The first and most ancient series consists of isolated vaults dating from the eighteenth to the twenty-second dynasty; that is to say, from about B.C. 1703 to B.C. 980. The second group, which dates from the reign of Sheshonk I (twenty-second dynasty, B.C. 980) to that of Tirhakah, the last king of the twenty-fifth dynasty, is more systematically planned, and consists of one long tunnel bordered on each side by a row of funereal chambers. The third belongs to the Greek period, beginning with Psammetichus I (twenty-sixth dynasty, B.C. 665) and ending with the latest Ptolemies. Of these, the first are again choked with sand; the second are considered unsafe; and the third only is accessible to travelers.