Valmiki Ramayana Yuddha Kanda Sarga 42 Shloka 21

कामरूपिणः who could change their form at will, इत्येवं in this manner, घोषयन्तश्च shouting, गर्जन्तश्च roaring, लङ्कायाः into Lanka, प्राकारं defensive walls, अभ्यधावन्त rushed over.

Shouting in that manner, the monkeys who could change their form at their will started roaring and rushed towards the defensive walls.