The Romans invented the calendar, which we most use to this day. The so-called Julian Calendar is a solar calendar developed at the request of Julius Caesar by the Greek astronomer Sosygenes and implemented in 709 AUC (45 BCE) as the calendar of the Roman state.
The Julian calendar was late (1 day in 128 years) compared to the astronomical one, so it was replaced by the current Gregorian calendar.
To this day, however, it is the basis of the liturgical year in the Orthodox Church.
IMPERIUM ROMANUM is in process of translation over 3300 Polish articles about history of ancient Rome. If you have the opportunity to financially support the further translations – even with smaller amount – I will be very grateful.