The boats in which they carry cargo are made of the acacia, which is most like the lotus of Cyrene in form, and its sap is gum. Of this tree they cut logs of four feet long and lay them like courses of bricks, and build the boat by fastening these four foot logs to long and close-set stakes; and having done so, they set crossbeams athwart and on the logs. They use no ribs. They caulk the seams within with byblus. There is one rudder, passing through a hole in the boat's keel. The mast is of acacia-wood and the sails of byblus. These boats cannot move upstream unless a brisk breeze continues; they are towed from the bank; but downstream they are managed thus: 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.