Claudius Ptolemy, the Greco-Egyptian geographer of Alexandria, wrote about a "Stone Tower" (λίθινος πύργος, Lithinos Pyrgos in Greek, Turris Lapidea in Latin) which marked the midpoint on the ancient Silk Road – the network of overland trade routes taken by caravans between Europe and Asia.
He refers to it just once more, in his gazetteer in Book VI when he details the Seventh Map of Asia, and on this occasion goes further to reveal its coordinates as longitude 135 and latitude 43 degrees north on his gradation system.
But the Stone Tower's actual location has been vigorously debated by researchers and historians over the centuries because, despite his coordinates, the information Ptolemy (and other scholars from his era) left behind is simply not precise enough.
If the Stone Tower could be pin-pointed then not only would this be of great significance to the study of ancient geography, but it would allow other important landmarks in this region, similarly (and imprecisely) detailed by Ptolemy, to be more closely located.
[11] From the turn of this century, Claude Rapin (2001)[12] has suggested it is Sulaiman-Too; while Paul Bernard (2005),[13] by carefully tracing the route taken by the caravan of Maes Titianos, locates the Stone Tower near Daraut-Kurgan; and Igor Vasilevich Piankov (2014),[14][2] after also considering information drawn from contemporary sailors, agrees with him.