bhu-mandalam idam vainyah
prayas cakre samam vibhuh
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
After this, the king of all kings, Maharaja Prthu, leveled all rough places on the surface of the globe by breaking up the hills with the strength of his bow. By his grace the surface of the globe almost became flat.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Generally the mountainous and hilly portions of the earth are made flat by the striking of thunderbolts. Generally this is the business of King Indra of the heavenly planets, but King Prthu, an incarnation of the Supreme Personality of Godhead, did not wait for King Indra to break up the hills and mountains but did so himself by using his strong bow.