The Imperial Jedi Temple garrison was a garrison of troopers were stationed at the Jedi Temple to guard it from looters, at least that was what they claimed. The real reason was that Palpatine placed them there after Order 66 and the Great Jedi Purge to eliminate any Jedi that came back to the Temple. However, even with such a substantial garrison guarding the Temple, they still were no much for the Sith-turned-freedom fighter, Galen Marek.