I don't know much about the Roman history, but a thought: There's a difference between crossing a sea and traveling on the sea skirting the coast (keeping the c

I don't know much about the Roman history, but a thought: There's a difference between crossing a sea and traveling on the sea skirting the coast (keeping the coastline always in sight). Shipping large amounts of grain from Egypt was vital for the livelihood of the populace of Rome the city, so there was some maritime know-how in the empire.