In the Return of the King during the Battle of the Pelennor Fields there was a great battering ram brought up by Sauron's Forces. The book doesn't say how tall it was. All it says it was as long as a great forest tree a hundred feet in length. I bet it was even bigger than that by the looks of it if you've ever seen the cartoon version 180's return of the king.

In the book it says " Up it rose, even to the level of the topmost circle, and there was crowned by the battlement: so that those in the citadel might, like mariners in a mountainous ship, look from its peak sheer down upon the gate 700 feet below". But as we see from the 1980's and 2003 film return of the king we know it has more levels and towers than that. The book really doesn't describe how tall the things built in middle earth really is though it gives some detail.

You do understand that these are works of fiction and that the moves used special effects and animation to portray these scenes.

If JRR Tolkien decided not to specify he was leaving it up to the imagination. The readers or the producers of the movies.

Grond was said to be 60 feet high, 150 feet long, and as thick around as an enormous tree.

Grond - Lord of the Rings Wiki (http://lotr.wikia.com/wiki/Grond)

The Citadel of Minas Tirith, with its White Tower, was three hundred feet high, so that its apex was one thousand feet above the plain.

Minas Tirith (http://lotr.wikia.com/wiki/Minas_Tirith)