The forces of the Enemy have brought a terrible weapon to Osgiliath, and you must destroy it before it can be used against Minas Tirith.
'Our enemies have brought a great weapon to Osgiliath, a mighty ram that bears the name 'Grond.' The message you recovered is addressed from Gothmog to 'the master of the great beasts,' and it commands this master to pull the ram through the city to the West-gate. We must assume that Gothmog or his superiors plan to use Grond to smash the gates of Minas Tirith.
'We have to stop it! If this message has not been delivered by another of Gothmog's runners, we have a brief window available to us before Grond begins to move once more. This hunter from the Blackroot Vale has been itching for a chance to prove himself. Take him and find Grond before it leaves the city, and damage or destroy the ram before it reaches the Pelennor. Once it leaves Osgiliath we will not be able to halt its progress, ${PLAYER}!'
Derufin can be found among the Osgiliath Culverts beneath the city.
Damrod has asked you and Derufin to find the great ram, Grond, and damage or destroy it before it is pulled out of Osgiliath into the Pelennor.
You managed to damage Grond, but learned an unsettling truth about the identity of Gothmog, a commander of the forces in Osgiliath.