The Black Watch is the elite unit of the Elven military whose sworn duty is to protect the Ellcrys and the Gardens of Life in which it resides. The Ellcrys holds the Demons behind the Forbidding to keep them from escaping into the Four Lands.
The Black Watch has been a military unit for centuries. There are Black Watch guards at the gate to the Gardens of Life at all hours. During the War of the Forbidding the Black Watch was a part of those who made the last stand against the Demons at the Gardens of Life, just before Amberle Elessedil restored the Ellcrys.