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All over India there are large numbers of rivers with extreme ebb-and-flood tides that at the time of the new moon and the full moon last for up to three days, diminishing during the intervals. They are much more extreme in the sea around Barygaza than elsewhere. Here suddenly the sea floor becomes visible, and certain parts along the coast, which a short while ago had ships sailing over them, at times become dry land, and the rivers, because of the inrush at flood tide of a whole concentrated mass of seawater, are driven headlong upstream against the natural direction of their flow for a good many stades.

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Thus the navigating of ships in and out is dangerous for those who are inexperienced and are entering this port of trade for the first time. For once the thrust of the flood tide is under way, restraining anchors do not stay in place. Consequently, the ships, carried along by its force and driven sideways by the swiftness of the current, run aground on the shoals and break up, while smaller craft even capsize. Even in the channels some craft, if not propped up, will tilt over on their sides during the ebb and, when the flood suddenly returns, get swamped by the first wave of the flow. So much power is generated at the inrush of the sea even during the dark of the moon, particularly if the flood arrives at night, that when the tide is just beginning to come in and the sea is still at rest, there is carried from it to people at the mouth something like the rumble of an army heard from afar, and after a short while the sea itself races over the shoals with a hiss.