Byzantium levied a toll on ships using this strait that opens into the Black Sea
[DOC] [TLE] Dictionary of Greek and Roman Geography (1854), BOSPORUS ... [PAR] Pomponius Mela (1.19.5) calls it canalis, and divides it into the strait ... of the 
Black Sea (Euxeinus), it may be observed, that the soundings which have been ... 
gave birth, was the fulfilment of a national desire to open the inhospitable Euxine.