Great Signal

Over the days leading up to the Battle of the Pelennor, the Fire-mountain of Orodruin in Mordor belched forth a red glow and emitted the dark vapours that would create the Dawnless Day for the people of Gondor. During this time, Frodo Baggins and Samwise Gamgee worked their way through Ithilien and towards the mountains of Ephel Dúath. As they entered Imlad Morgul on 10 March III 3019, the shaking of the ground suddenly increased to a powerful quaking, and a burst of brilliant red fire - presumably unleashed from Mount Doom¹ - shone out from Mordor to illuminate the clouds, as the air was filled with the sound of a thunderclap.

This was the Great Signal, the sign to Sauron's soldiers to begin their march to war. From Minas Morgul, close by the hiding place of Frodo and Sam at the time, an answering signal went up: a storm of blue lightning flashing up into the sky from the Tower and its surrounding hills, while a hideous screech echoed off the rocks of the valley. At that, the armies of the Witch-king began their progress out from their city and on the road that would lead them to the Battle of the Pelennor. Though dreadful to experience for the Hobbits at the time, the Great Signal provided the distraction they needed to slip past Minas Morgul and begin the ascent of the Stairs of Cirith Ungol that would lead them into Mordor.