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 that it was meant to, before being trapped in a circle of cameras and monitors by the Fifth Doctor. (AUDIO: The Cradle of the Snake) Later, 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)

Three hundred years later, in 2926, the Federator banished the Mara to the Dark Places of the Inside. (TV: Snakedance) possessing Tegan Jovanka on Deva Loka, (TV: Kinda) the Mara used her to pilot the Doctor's TARDIS to Manussa in its year 3426, 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
Dates are based on the Great Crystal being 800 years old. In addition, Ambril states the middle Sumaran Era was 700 years ago.