Mordor Catapult

"As soon as the great catapults were set, with many yells and the creaking of rope and winch, they began to throw missiles marvelously high, so that they passed right above the battlement and fell thudding within the first circle of the City; and many of them by some secret art burst into flame as they came toppling down"
The Lord of the Rings, Book Five the War of the Ring, The Siege of Gondor.

The Mordor Catapult, assisted by a troll to load the heavy stone, that will crash against the City of Minas Tirith.

This will give my Mordor force some hard hitting artillery power from long range.