Pliny the Elder, Natural History 6.106

6.106

ex India renavigant mense Aegyptio Tybi incipiente, nostro Decembri, aut utique Mechiris Aegyptii intra diem sextum, quod fit intra idus Ianuarias nostras: ita evenit ut eodem anno remeent. navigant autem ex India vento volturno et, cum intravere Rubrum mare, Africo vel austro. nunc revertemur ad propositum.

Travellers set sail from India on their return to Europe, at the beginning of the Egyptian month Tybis, which is our December, or at all events before the sixth day of the Egyptian month Mechir, the same as our ides of January: if they do this, they can go and return in the same year. They set sail from India with a south-east wind, and upon entering the Red Sea, catch the south-west or south. We will now return to our main subject.