rāmaḥ Rama, saumitriṇā saha with Saumitri, tasya śailasya mountain's, śikharē on the top, mahatīm great/ long, āyatām wide, guhām cave, vāsārtham to reside, pratyagṛhṇata decided to reside.
Rama and Lakshmana decided to reside in the long, wide cave on top of the great mountain.