Method of Bridging Rivers. How Alexander constructed his bridge over the river Indus, is explained neither by Aristobulus nor Ptolemy, authors whom I usually follow; nor am I able to form a decided opinion whether the passage was bridged with boats, as the Hellespont was by Xerxes and the Bosporus and the Ister were by Darius,663 or whether he made a continuous bridge over the river. To me it seems probable that the bridge was made of boats; for the depth of the water would not have admitted of the construction of a regular bridge, nor could so enormous a work have been completed in so short a time.664 If the passage was bridged with boats, I cannot decide whether the vessels being fastened together with ropes and moored in a row were sufficient to form the bridge, as Herodotus the Halicarnassian says the Hellespont was bridged, or whether the work was effected in the way in which the bridge upon the Ister and that upon the Celtic Rhine665 are made by the Romans, and in the way in which they bridged the Euphrates and Tigres, as often as necessity 278compelled them. However, as I know myself, the Romans find the quickest way of making a bridge to be with vessels; and this method I shall on the present occasion explain, because it is worth describing. At a pre-concerted signal they let the vessels loose down the stream, not ............