Naturalis historia 6.83

6.83

siderum in navigando nulla observatio; septentrio non cernitur. volucres secum vehunt emittentes saepius meatumque earum terram petentium comitantur. nec plus quaternis mensibus anno navigant. cavent a solstitio maxime centum dies, tune illo mari hiberno.

For this reason it is that the vessels are constructed with prows at either end; so that there may be no necessity for tacking while navigating these channels, which are extremely narrow. The tonnage of these vessels is three thousand amphoræ. In traversing their seas, the people of Taprobane take no observations of the stars, and indeed the Greater Bear is not visible to them; but they carry birds out to sea, which they let go from time to time, and so follow their course as they make for the land. They devote only four months in the year to the pursuits of navigation, and are particularly careful not to trust themselves on the sea during the next hundred days after our summer solstice, for in those seas it is at that time the middle of winter.