Polyphemus is described to be as tall as the clouds

Battalions of Cyclopians came like a flood. In battle, these with weaponless hands cast hills for their stony spears, and their shields were cliffs; a peak from some mountain-ravine was their crested helmet, Sicilian sparks were their fiery arrows. They went into battle holding burning brands and blazing with light from the forge they knew so well – Brontes and Steropes, Euryalos and Elatreus, Arges and Trachios and proud Halimedes. One alone was left behind from the war, Polyphemos, tall as the clouds, so mighty and so great, the Earthshaker’s own son; he was kept in his placee by another love, dearer than war, under the watery ways, for he had seen Galateia7 half-hidden, and made the neighbouring sea resound as he pouredc out his love for a maiden in the wooing tones of his pipes.

DIONYSIACA, Book 14, Translated by W. H. D. Rouse.