From this description of the mode in which the Roman aqueducts were constructed, it is obvious that the principles and precautions, which, as is sometimes supposed modern science has discovered and applied to such structures, were known and used at that early day. The declivity given to the channel was indeed greater than that usual in more modern conduits, but in other respects, few or no improvements or alterations in the manner of building and securing such works, seem to have been made.

It will, however, strike the reader with surprise, to find that leaden pipes were used

and found equal to resist the pressure of columns of water, even in passing it down and up steep declivities. In subsequent pages, some remarkable instances of this will be presented. Iron pipes seem to have been wholly unknown to the Romans. Indeed, the first

castings of iron we hear of, were made in England, as is related by Baker, in his Chronicles of the Kings of England, about the year 1545, in the 35th year of Henry VIII.,

by Ralph Hage and Peter Bawde. Pipes of cast iron are now the only ones used for mains, or large distributing pipes. These may be made of almost any diameter, by duly increasing the quantity of metal contained in them. The largest pipes laid down in this city, are of three feet internal diameter, and in lengths of nine feet, weighing from 3,500 to 3,800 Ibs. The largest diameter of leaden pipes used by the Romans, was of 12 inches internal bore.