Some years ago, I noticed that the Wikipedia entry for that year claims that the building work on Hadrian's Wall began on September 13. I have always wondered where that date came from.
Ancient exploits cannot usually be pinned down so accurately. But we often know the precise dates of important events, like births, deaths and battles. Hadrian's birthday, for example, was 24 January. He came to the throne on 10 August, at the age of 41½, in AD 117. And he died on 10 July, twenty-one years later.
A building project is rather more difficult to date. When does work actually begin? I'm sure that Hadrian did not chip the first stone or snip a stretched-out ribbon. So how would we define the date of commencement anyway?
If such a precise date is unlikely for the building of a 80-mile wall, where did it come from? I suppose a construction project undertaken by the Roman army might well have begun at the end of the campaigning season. For the Romans, summer officially ended in September, so the military headed back to base then. But the vernal equinox, the most obvious sign of that event, fell some ten days after our date of 13 September. On this reasoning, work really ought to have begun on Hadrian's Wall around 24 September.
Beware the Ides
So why September 13? In the worst Wikipedia fashion, no authority is cited, no evidence given, so we cannot say where the Wikipedia article's author got the idea from. Certainly, at Rome, September was a busy month, with the festival of the Ludi Romani, the Roman Games. But these fell throughout the fortnight from September 5 until September 19. So our date of September 13 has no particular significance on that score. But it does have significance as the idus Septembri, the Ides of September. This particular day was notable as the Epulum Jovis, or Feast of Jupiter, commemorating the foundation of the oldest temple in Rome, the great Temple of Jupiter Optimus Maximus ("best and greatest"). This auspicious date was also the day on which the beloved emperor Titus died in AD 81 (curiously, at the age of 41½), which was perhaps further cause for celebration, as a new god joined the Roman pantheon.
But, if we've established that 13 September was a notable date for the Romans, it is still a complete mystery why the Wikipedia author has chosen it as the foundation date for Hadrian's Wall. (Unless you know differently ...)