Who were the best Greek or Roman navigators and why?

Rather, the Greeks, in this way, during the period of the great Greek colonization, they were able to spread their trade and political influence over a vast territory from the south of Spain to the modern town of Poti in Georgia (they founded and named it Phasis), and also created colonies in the steppes of the Black Sea region (Olbia, Gorgipia, Chersonesos).
They also had a solid fleet with a small size of the policies themselves, and in Sparta (the state of Lacedaemon), shipbuilding was not developed. The Romans, despite the enormous size of their empire, could not advance anywhere further than the Greeks, for example, to the equator. Unless they sailed to Britain.