Then with a crash came a great ringing shout: ra-hoom-rah! The trees quivered and bent as if a gust had struck them. There was another pause, and then a marching music began like solemn drums, and above the rolling beats and booms there welled voices singing high and strong.

We come, we come with roll of drum: ta-runda runda runda rom!

The Ents were coming: ever nearer and louder rose their song:
We come, we come with horn and drum: ta-rûna r na r na rom!

‘Hoom, hom! Here we come with a boom, here we come at last!’ called Treebeard when he caught sight of Bregalad and the hobbits. ‘Come, join the Moot! We are off. We are off to Isengard!’.
‘To Isengard!’ the Ents cried in many voices.
‘To Isengard!’

To Isengard! Though Isengard be ringed and barred with doors of stone;
Though Isengard be strong and hard, as cold as stone and bare as bone,
We go, we go, we go to war, to hew the stone and break the door;
For bole and bough are burning now, the furnace roars - we go to war!
To land of gloom with tramp of doom, with roll of drum, we come, we come;
To Isengard with doom we come!
With doom we come, with doom we come!