Gaius Julius Caesar arrived in the world on July 13, 100 B.C., but, contrary to popular belief, it’s unlikely he was born by caesarean section. Although the procedure existed at the time, it was usually fatal to the mother and therefore only performed when a pregnant woman was dead or dying, in an effort to save a child. In fact, Caesar’s mother, Aurelia, lived until 54 B.C., nearly half a century after her son’s birth.

According to some sources, the origin of the Caesar name is attributable to one of Caesar’s forebears who was “caesus,” (Latin for “cut”) from his mother’s womb. Other origins of the name have been suggested, including the possibility that the founding member of Caesar’s family branch might have had “caesaries,” or long, flowing hair.

In 75 B.C., Caesar, then in his mid-20s, set out from Rome for the Aegean island of Rhodes, a noted center of learning where he planned to study with Apollonius, a Greek rhetorician whose students had included Cicero, who became one of ancient Rome’s most famous orators. However, along the way to Rhodes, Caesar’s ship was hijacked by pirates off the southwestern coast of Asia Minor. When his captors named a ransom price for his release, Caesar thought the number was insultingly low and insisted a greater sum be demanded. Eventually, the higher figure was raised and Caesar was freed. Soon after, he sought revenge against his former captors by commandeering a group of ships and men to help him hunt down and swiftly capture the buccaneers, who he then had executed.

Caesar married his first wife, Cornelia, in 84 B.C., when he was a teenager. Within several years, a general named Lucius Cornelius Sulla became dictator of the Roman republic and ordered the execution of anyone he considered an enemy of the state. Caesar’s father-in-law, Lucius Cornelius Cinna (d. 84 B.C.), had been a rival of Sulla. As a result, Sulla ordered Caesar to divorce Cornelia, but Caesar refused. Knowing such defiance could cost him his life, Caesar fled Rome and became a fugitive. During his time on the run, he contracted malaria and later was caught by one of Sulla’s men, who forced Caesar to pay him a huge bribe, almost all of his money, in order to remain free. Eventually, some of Caesar’s influential friends and relatives persuaded Sulla to let Caesar return to Rome, where he was reunited with Cornelia. The couple had a daughter, Julia Caesaris, in 76 B.C.

In 48 B.C., Caesar went to Egypt to track down one of his rivals, the Roman general Pompey, and while there he met Cleopatra, who was embroiled in a civil war with her younger brother and co-ruler Ptolemy XIII (per ancient Egyptian custom, the two ruled under the formal title of husband and wife). Caesar, who declared himself executor of the will of the siblings’ late father, ordered the pair to come see him so they could settle their feud. When Ptolemy’s army stopped Cleopatra from traveling to the palace where Caesar was staying, she had herself smuggled in a laundry bag to meet him for the first time, according to some accounts. Caesar and Cleopatra, who was half the Roman general’s age, became romantically involved, and around 47 B.C., she gave birth to a boy, Ptolemy Caesar, who was believed to be Caesar’s child. The Egyptians referred to him as Caesarion, meaning little Caesar.

Shortly after Caesar’s murder in 44 B.C., Cleopatra’s brother and co-ruler Ptolemy XIV was killed. (Her previous co-ruler, Ptolemy XIII, had died around 47 B.C.) Although never proven, there was suspicion Cleopatra poisoned Ptolemy XIV so she could name Caesarion her co-ruler, which she did that same year. He became known as Ptolemy XV.

In 31 B.C., the forces of Cleopatra and her lover Mark Antony were defeated at the Battle of Actium by Octavian, Caesar’s great nephew and chosen heir. The following year, Antony and Cleopatra both committed suicide, leaving Caesarion as Egypt’s sole pharaoh; however, his reign was brief because not long after his mother’s death, Caesarion was murdered on orders from Octavian, who went on to become the first Roman emperor. Taking the name Augustus, he ruled from 27 B.C. to A.D. 14.

Caesar had no other known sons besides Caesarion. His only known daughter, Julia, died in childbirth in 54 B.C.

Before Caesar came to power, the Romans used a calendar system based on the lunar cycle, which dictated that there were 355 days in a year. This system was 10 ¼ days shorter than a solar year, the amount of time required for the Earth to make one complete revolution around the sun. Although Roman officials were supposed to add extra days to the lunar calendar every year at their discretion in order to keep it aligned with the seasons, this didn’t always happen and, as a result, the calendar was confusing, out of whack with the seasons and ripe for abuse by politicians interested in extending their terms in office.

After consulting with the astronomer Sosigenes, Caesar implemented a new system, the Julian calendar, which went into effect in 45 B.C. and was made up of 365 days in a year. The calendar was intended to be in sync with the solar cycle; however, because the actual solar year is 365 ¼ days long, Caesar also added an extra day, called a leap day, every four years to make up the difference.

The Julian calendar remained the standard until the late 16th century, when a slightly modified version of the system, known as the Gregorian calendar, was introduced. Today, the Gregorian calendar is the world’s most widely used civil calendar.