September wears its history in its name: septem, seven, the seventh month of the old Roman year that opened in March, a number it kept even after January and February were set ahead of it and the count slipped by two. The same is true of its three companions, October, November and December, so a third of the modern year still counts itself from a first month that has not been first for well over two thousand years.
Emperors repeatedly tried to claim the month and failed. Caligula renamed September Germanicus for his father; Domitian, born in October, took September as Germanicus and October as Domitianus for himself; the Senate offered Tiberius the month and he refused it, reportedly asking what they would do when there were more emperors than months. Every one of these names was abandoned, most of them the moment their author fell, and the plain number outlasted the whole dynasty of vanities, which is why the failed renamings are remembered chiefly as a lesson in how calendars resist power.
In the Roman religious year the month belonged to Jupiter. The Ludi Romani, the oldest and greatest of the public games, filled its middle weeks, and at their heart on the thirteenth stood the epulum Iovis, the banquet of Jupiter, at which the images of the Capitoline triad reclined at table with the magistrates of Rome. The games had begun as a votive offering vowed before battle and became the fixed centrepiece of the civic religion's autumn.