Histories

they have a raft made of tamarisk wood, fastened together with matting of reeds, and a pierced stone of about two talents' weight; the raft is let go to float down ahead of the boat, connected to it by a rope, and the stone is connected by a rope to the after part of the boat.

So, driven by the current, the raft floats swiftly and tows the “baris” (which is the name of these boats,) and the stone dragging behind on the river bottom keeps the boat's course straight. There are many of these boats; some are of many thousand talents' burden.