Valmiki Ramayana Yuddha Kanda Sarga 4 Shloka 39

सागरौघनिभम् expansive as the ocean, भीमम् dreadful, महत् great, तत् that, वानरबलम् vanara strength, भीमकोपस्य one whose wrath creates fear, रामस्य Rama's, शासनम् command, ज्ञात्वा knowing, भीतवत् on account of fear, नगराभ्याशान् parts of the city, तथा so also, जनपद villages, वर्जयत् avoiding, महाघोषम् great sound, भीमघोषम् frightening sound, आर्णवम् इव like the ocean, उत्ससर्प went on.

The dreadful vanara army expansive as the ocean went knowing about the fear of Rama's wrath. They went avoiding parts of cities and villages making frightening sounds like the great sound of the waves of the ocean.