Over these shallows a pier or causeway was built, which finally became a broad and inhabited neck.

The principal part of the ancient city, however, was on the main land.
The curvature of the earth requires that a light-house on a coast should have a considerable elevation, otherwise its summit would not appear above the horizon, unless the mariner were very near.

To attain this elevation, the architects usually take advantage of some hill or cliff, or rocky eminence near the shore.

There was, however, no opportunity to do this at Pharos; for the island was, like the main land, level and low.

The requisite elevation could only be attained, therefore, by the masonry of an edifice, and the blocks of marble necessary for the work had to be brought from a great distance.