The names of the months and days are still those of ancient Rome; the way we measure time and hours was created by the Romans with a first calendar of ten months only, which can be traced back to Romulus.

King Numa added two more moths, but the overall number of days was too high and over the centuries led to a discrepancy between the date and the seasons.

After the Roman conquest of Egypt, Rome came into contact with the Alexandrian astronomers who were the best in the world and had learned their science and wisdom from the Babylonians.

To correct the calendar, since winter then fell into the summer months, Julius Caesar called an Alexandrian astronomer, Sosigenes, to reform the calendar.

Thus was born the Julian Calendar with a year of 365.25 days, and introduced an extra day every four years, which was inserted as an additional sixth day before the calends of March, and therefore called bis-sextus day (hence the term "bisestile" that  is leap year).
In 44 BC after Caesar's death, the month Quintilis of the Numa calendar was renamed Iulius (June) in his honor.

Between 10 and 9 BC. Augustus inaugurated the Ara Pacis, to celebrate the Pax Augusta that he had brought back to the empire after a century of civil wars.
On that same date he inaugurated the Horologium Augusti, a gigantic sundial whose gnomon was an obelisk from Egypt, which today is located in the Montecitorio square in Rome.
The obelisk was used to check the accuracy of the Calendar and to correct errors due to the irregular application of the leap year.

The obelisk was dedicated to the Sun, as the inscription explains: «The emperor Caesar Augustus, son of the divine Caesar, emperor for the twelfth time, consul for the eleventh time, tribune for the fourteenth time, together with Egypt given in the power of the Roman people dedicated this gift to the Sun».

The Horologium was such a marvel that Pliny the Elder (who lived in the 1st century AD and saw it work) described it in detail, passing down the name of the mathematician who had designed it, Facundus Novus:
«The divine Augustus attributed the marvelous function of capturing the shadows of the Sun to the obelisk in the Campus Martius, thus determining the length of the days and nights.
He had a stone slab placed which was proportionate to the height of the obelisk so that, in the sixth hour of the day of the Winter Solstice (December 21st), its shadow was as long as the slab, and slowly diminished day after day, to then grow again, following the bronze rulers inserted into the stone: a device that is worth knowing, and which is due to the genius of the mathematician Facundus.
The latter placed a golden sphere on the tip of the pinnacle, the end of which projected a shadow gathered within itself, because otherwise the tip of the obelisk would have created an irregular shadow (it was, they say, the human head that gave him the idea) ».

In the Capitoline Museum in Rome there is a gilded bronze globe with a pinnacle, which is probably the original one that was on top of the obelisk.

In 8 BC the month Sextilis of the Numa calendar was renamed Augustus (August) in honor of Augustus himself.
The Julian calendar remained in use for centuries, even after the fall of the Roman Empire, and was replaced in 1582 by the Gregorian calendar – the one we still use today.
Thanks to new and more precise astronomical calculations of the duration of the solar year, to correct the error accumulated over the centuries, two weeks were deleted.