According to Companion Guide to Istanbul: And Around the Marmara by John Freely and Susan Glyn, there is a place on the European side of the Bosphorus in Istanbul which is so treacherous even the crabs avoid it.
The current off Akinti Burnu is the strongest of any point on the European side (of the Bosphorous), reaching a speed of over five knots when the prevailing north wind is blowing. This made it very difficult for sailing vessels to round Akinti Burnu on their way up the Bosphorus, and they had to be pulled around the point by porters on the shore. Apparently crabs also found it difficult, as Gyllius writes in his book on the Bosphorus: “I myself saw there stones worn down by the long procession of crabs. And even if I had not seen it I would not have thought it far from the truth that stones should be worn down by the hard claws of crabs, since we see that ants can dig down furrows and make a bath by the continuous attrition of their feet.”
The author Freely and Glyn quote is Petrus Gyllius or Pierre Gilles, born in France in 1490:
IN 1544 Gilles left France with a French embassy that included the king’s royal cosmographer, André Thevet d’Angoulême. Gilles seems to have spent the years 1544 to 1547 in Constantinople, gathering literary sources and investigating the physical remains of the ancient city. Out of money, in 1548 he enlisted in Suleyman’s army and joined the expedition against Persia. In 1548 he met the French ambassador to the Sublime Porte, Gabriel d’Aramon, who took Gilles with him to the Holy Land and Egypt.
IN JANUARY 1550, still in d’Aramon’s company, Gilles returned to Constantinople. That same year he travelled with the ambassador back to France. Almost immediately upon his return, however, Gilles headed south to Rome. While in Rome Gilles began the work of sifting through the large number of source materials and notes that he had accumulated on the history of Constantinople. Gilles had made great progress in completing his book on Constantinople by 1555; but then, as the epitaph on his tomb tells us, he was stricken by a fever that he fought for eleven days before dying at the fourth hour on January 5, 1555. His patron Georges d’Armagnac provided for his funeral and his tomb, in the church of San Marcello in Rome.
FROM HIS EPITAPH we learn that Gilles was hard at work organizing his notes for his two works on Constantinople when he died. He apparently left these incomplete; and his nephew, Antoine Gilles, then took up the task of finishing his work. This he did faithfully; and in the 1560s a string of books emerged from his stewardship. The most important for our purposes appeared in Lyon in 1561 and were Gilles’ Three Books on the Thracian Bosporus and the Topography of Constantinople and Its Antiquities in Four Books.