Manussan year

The Manussan year was the time scale used by the inhabitants of Manussa.

On New Year's, 2215, the Mara, having travelled back in time, tried to upset the Web of Time by overthrowing Manussa earlier than it was meant to, but was trapped in a circle of cameras and monitors by the Fifth Doctor. (AUDIO: The Cradle of the Snake)

In 2326, the Mara manifested through its original creation via the Great Crystal, and the Manussan Empire was replaced by the Sumaran Empire. (AUDIO: The Cradle of the Snake)

In 2926, the Federator banished the Mara to the Dark Places of the Inside. (TV: Snakedance)

In 3426, the Mara, while possessesing Tegan Jovanka, used her to pilot the Doctor's TARDIS to Manussa, where it planned its Becoming on the 500th anniversary of its defeat. (TV: Snakedance)

In 9235.3, the Jovians celebrated the Millennium Mardi Gras. (AUDIO: Neverland)

Behind the scenes
There is a slight error in dating in that the Great Crystal is said to be 800 years old, but Federation records begin six hundred years after the fall of the Manussan Empire, so it should be 1100 years old.