What have the Romans ever done for us? Well, beyond cement, sanitation, and all of those straight roads, the Romans played a big role in how we celebrate Christmas. Or, certainly, their wintertime traditions have mutated and been absorbed into what comes to mind when we think of festive fun.

Here are three elements of Roman mid-winter celebrations that are either reminiscent of or directly responsible for our modern Christmas traditions.

Mithraism

Temple of Mithras, Carrawburgh Roman Fort, Hadrian’s Wall, Northumberland, England. Roman civilization, 3rd century C.E. Photo: DeAgostini/Getty Images.

Like for many of us, the 25th of December was a major feast day for followers of the Cult of Mithras. An ancient Iranian god of the sun, originally called Mithra, Mithras was absorbed into Greco-Roman belief as the central figure for a mysterious cult that worshipped him between the 1st and 4th centuries C.E. Most imagery of Mithras shows the god slaughtering a bull (other images show him at a banquet feasting on the meat from the slaughtered bull), while other iconography shows him being born from a rock.

Ritual meals taken together were a key part of Mithraism, and followers would walk over the charcoal of the remaining scraps and bones to blacken their feet. The cult spread far throughout the west of the Roman Empire, including Roman Africa and Roman Britain. In Roman Britain, along Hadrian’s Wall—built by the emperor to separate Roman territory from the tribes of Caledonia—a “Mithraeum” stands in the Roman fort of Carrawburgh. Mithraeums were designed to be reminiscent of the cave in which Mithras was said to have slaughtered his bull, and Roman military leaders (a group with whom Mithraism was popular) would have gathered there to celebrate the feast days, including December 25th.

Sigillaria

A market scene in ancient Pompeii before its destruction in the eruption of Mount Vesuvius in 79 C.E. From Hutchinson’s History of the Nations (1915). Photo: Universal History Archive/Universal Images Group via Getty Images.

Saturnalia was an annual Roman Pagan festival, named after the god of agriculture, Saturn, who was worshipped during the mid-December celebration. The festival is believed to be the source of many modern Christmas traditions, including wreaths made from holly and ivy, caroling, and advent candles. And much in the same way that Christmas seems to creep into shops earlier and earlier each year nowadays, Roman statesmen tried to limit the number of days that Saturnalia was celebrated as it expanded from a single day into a week or more.

In late December, at the end of Saturnalia, Romans—including Emperors—would celebrate a day of gift-giving called Sigillaria. “Sigillaria” means “day of little figures”; the exchange of small figurines, usually made from terracotta, wood, or wax, was traditional. It isn’t clear whether these figurines had religious significance (some were in the form of gods and goddesses) or whether they were simply trinkets (others were of animals, for example). Pop-up markets (which these days are pretty much impossible to avoid) were even set up to sell gifts, with Rome’s Via Sigillaria so named because it hosted such markets.

The Julian Calendar

Pelagio Palagi, Julius Caesar Dictating the Commentaries (1813). Photo: DEA/V. Pirozzi/Getty Images.

Julius Caesar proposed his new Julian calendar in 46 B.C.E., to better line up with the equinoxes. Caesar’s new year began the following year on January 1, which for the first time was the first day of the year; the first of the year had previously fallen in March, to coincide with the coming of spring. This made 46 B.C.E. a whopping 445 days long. Caesar proposed a 365-day year with a leap day every four years, which differed from the previous 355-day year with an occasional additional 27-day month—called Mensis Intercalaris—added between February and March.

The reorganization moved the Winter Solstice, a day long celebrated with feasts and libations, to December 25. This was celebrated as “Dies Natalis Solis Invicti” (“the birthday of the unconquerable sun,” possibly a reference to the god Mithras) and by the 4th century C.E., when Christianity became the official religion in the Roman Empire, the date of the birth of Jesus was subsumed into these pre-existing December 25th practices.