The Byzantine sundial: telling the time in the 6th century
4 Video Views·May 17, 2025
This ancient mechanical calendar is the second oldest geared device ever discovered.
It included both a sundial for telling the time and a geared calendar, driven by a dial showing the seven days of the week. Although only these fragments survive, evidence suggests that it may have been used to convert between a popular calendar based on the phases of the Moon and the official Sun-based calendar of the Byzantine Empire.
This is a real jewel of the Science Museum Group collection.
It may not look like much, but this is the second oldest geared mechanism ever discovered.
It's called the Byzantine sundial calendar, and it dates from the 6th century AD from the Mediterranean.
It could be used to tell the time of day and keep track of the date.
We only have fragments of the original instrument, but originally there would have been a shadowcaster mounted on this plate,
which you could use to tell the time of day from the position of the sun in the sky.
And then this smaller wheel here has seven symbols representing the seven planets of the seven days of the week.
Originally you would have turned a lever each time a day passed, which would have driven the gears inside the calendar,
and on the back it would have displayed the date in the solar and the lunar calendar.
It's amazing to think this sophisticated mechanical calendar is 1,500 years old.