The Lord President wearing the Sash of Rassilon. (DW: The Deadly Assassin)
The Sash of Rassilon gave those who wore it protection from the gravitational and energy forces which emanated from the Eye of Harmony. It also allowed for some control of the Eye of Harmony. However, it had less power than its reputation suggested and would not have saved the Master had he opened the Eye fully. (DW: The Deadly Assassin)
It was one of the many Artefacts of Rassilon which were given to a newly elected President of the High Council. It was also a sacred item and the Time Lords bowed down to it. (DW: The Invasion of Time)