When a joint city was thus compacted and called Rome—­possibly its old Pelasgic appellation—­the first effort of the confederated settlements was to drain the geological lake in the centre of the city into the Tiber, a quarter of a mile distant.  This they did by means of the celebrated Cloaca Maxima, a part of which may be seen open at the present day under the pavement of the Roman Forum, near the Temple of Castor and Pollux.  This common sewer of Rome is one of its oldest and greatest relics.  It was built by the first Tarquin, the fifth king of Rome, a century and a half after the foundation of the city; and although two thousand five hundred years have passed away since the architect formed without cement its massive archway of huge volcanic stones found on the spot, and during all the time it has been subjected to the shock of numerous earthquakes, inundations of the Tiber, and the crash of falling ruins, it still serves its original purpose as effectually as ever, and promises to stand for as many ages in the future as it has stood in the past.  It is commonly said that we owe the invention of the arch to the Romans; and this work of undoubted Etruscan architecture is usually considered as among the very first applications of the principle.  But the arched drains and doorways discovered by Layard at Nineveh prove that the Assyrians employed the arch centuries before Rome was founded.  It had however only a subordinate place and a very limited application in the ancient architecture of the East; and it was left to the Romans to give it due prominence in crossing wide spaces, to make it “the bow of promise,” the bridge over which they passed to the dominion of the world.  The Cloaca Maxima is a tunnel roofed with two concentric rings of enormous stones, the innermost having an interior diameter of nearly fourteen feet, the height being about twelve feet.  So capacious was it that Strabo mentions that a waggon loaded with hay might find room in it; and it is recorded that the Consul Agrippa passed through it in a boat.  The mouth of the Cloaca opens into the Tiber, near the little round temple of Hercules in the Forum Boarium; but it is often invisible owing to the flooding of the river; and even when the Tiber is low, so much has its bed been silted up that only about three feet below the keystone of the sewer can be seen.  Subsequently all the sewers of Rome were connected with it; and at the present day the nose gives infallible proof that it carries off a very large portion of the pollution of the modern city.

By the Cloaca Maxima, the valley between the Capitoline and Palatine Hills was for the first time made dry land; all indeed, except a small swamp which remained in one corner of it to a later age, and which the great sewer was not deep enough to drain entirely.  Reeds grew around its margin, and boats were employed to cross it, as Ovid tells us.  The name Velabrum—­from an Etruscan root, signifying water, occurring in some