Strabo Geography 17.1.50

[50] We came from Syene to Philae in a waggon, through a very flat country, a distance of about 100 stadia. ¹ Along the whole road on each side we could see, in many places, very high rocks, round, very smooth, and nearly spherical, of black hard stone, of which mortars are made: each rested upon a greater stone, and upon this another: they were like hermaea. ² Sometimes these stones consisted of one mass. The largest was not less than twelve feet in diameter, and all of them exceeded this size by one half. We crossed over to the island in a pacton, which is a small boat made of rods, whence it resembles woven-work. Standing then in the water, (at the bottom of the boat,) or sitting upon some little planks, we easily crossed over, with some alarm indeed, but without good cause for it, as there is no danger if the boat is not overloaded.