Guards of the Citadel
The Guards of the Citadel were those honoured guards of Minas Tirith who were charged with protecting the Citadel, the highest and most important tier of the city. At the end of the Third Age, they were the only soldiers of the city to be liveried in the arms of Elendil himself - a white tree in blossom, surmounted by a silver crown and stars, all embroidered on a field of black. They also bore heirlooms of Gondor's ancient wealth, tall helmets wrought out of mithril, and bearing the carved wings of sea-birds. The numbers of these Guards is not known, but there seem to have been at least three companies (at least, one of their number - Beregond - is said in The Lord of the Rings to belong to the Third Company).
In the past, they had watched over the White Tree that stood in the Court of the Fountation, though at the time of the War of the Ring, that Tree had been dead for nearly one hundred and fifty years. After the War, the new King Aragorn Elessar, with the aid of Gandalf, found a new seedling of the Tree, and the Guards' great duty was refounded.