Valmiki Ramayana Yuddha Kanda Sarga 75 Shloka 23
Original Shlokaज्वलनेनपरीतानिनिपेतुर्भवनान्वथ । वज्रिवज्रहतानीवशिखराणिमहागिरेः ।।6.75.23।।
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ज्वलनेन burnt, परीतानि by fire, निपेतुः fell down, भवनानि mansions, महागिरेः large mountain, वज्रिवज्रहतानीव burnt by thunderbolt, शिखराणि peaks, यथा that way, महागिरेः like huge mountains.
The mansions burnt by fire fell down like a huge mountain struck by a thunderbolt.