Isengard was the stronghold of Saruman, an ally (servant) of Sauron of Mordor. Saruman used Orcs to assault Helm's Deep. But they were defeated and destroyed and Isengard itself was attacked by an army of Ents with the help of Merry and Pippin.
This is one of Mithril's older figures and exemplifies the timeless nature of the figures. I just ordered a number and they are still amazing