Lord Rama, during his attempt to cross the ocean,prayed Samudra Raja, Lord of the ocean.
He did not turn up.
In a rare display anger Lord Rama sent in His arrow and it landed and parched the place it fell.
Thus was formed the Maru Desert near Jaisalmer.
Ramayana says thus.
The valiant ocean, the lord of rivers, wearing a wreath of pearls, with his eyes resembling lotus leaves, bearing a beautiful garland made of all kinds of flowers on his head, with ornaments of refined gold, adorned with excellent jewels made of pearls from his domain, decorated with different kinds of gems and metals, resembling Himavat mountain, wearing on his broad chest a locket shedding a white luster, resembling a Kaustubha gem (adorning the blossom of Lord Vishnu) and hanging in the middle of a single string of pearls, with a multitude of waves whirled around him, encircled by the clouds and winds, escorted by rivers mainly the Ganga and Sindhu, endowed with diverse forms resembling various deities, approached Rama with joined palms, who stood with arrows in hand, addressing him first as ‘Rama!’ and spoke the following words: “O, beloved Rama! Earth, wind ether, water and light remain fixed in their own nature, resorting to their eternal path. Therefore, I am fathomless and my nature is that it is impossible of being swum across. It becomes unnatural if I am shallow. I am telling you the following device to cross me. Neither from desire nor ambition nor fear nor from affection, I am able to solidify my waters inhabited by alligators. I shall make it possible to see that you are able to cross over. I will arrange a place for the monkeys to cross me and bear with it. As far as the army crosses me, the crocodiles will not be aggressive to them.”
Then, Rama spoke to that ocean as follows: “Listen to me. This great arrow should not go in vain. In which region should it be descended?”
Hearing Rama’s words and seeing that powerful arrow, the large splendid Ocean spoke the following words to Rama: Towards my northern side, there is a holy place. It is well known as Drumatulya, in the same way as you are well known to this world. Numerous robbers of fearful aspect and deeds, having the sinful Abhiras as their chief, drink my waters there. I am not able to bear that touch of those wicked people, the evil doers, O, Rama! Let this excellent arrow with out vain be released over them there.”
Hearing those words of the high-soled Ocean, Rama released that excellent and splendid arrow towards that place as directed by the ocean. The place where the arrow, whose splendor was akin to that of a thunder and a thunder bolt, was descended by Rama- that place is indeed famous as desert of Maru* on this earth.
* Maru—Malwar in Rajastan (India)
The earth there, pierced by the dart, then emitted a sound . The waters of the penultimate subterranean region gushed forth from the mouth of that cleft. Then the hollow became known as Vrana. Water constantly seen, gushing forth from it resembled seawater. A terrific splitting sound was born in that place. Water was dried up in those cavities, as a result of hurling of that arrow by Rama. That desert of Maru became famous in the three worlds. Rama (the son of Dasaratha), a wise man and a valiant man resembling a celestial, made that cavity dried up and gave a boon to that desert of Maru. Due to granting of a boon by Rama, that desert of Maru became the most congenial place for cattle rearing, a place with a little of disease, producing tasty fruits and roots, with a lot of clarified butter, a lot of milk and various kinds of sweet- smelling herbs. Thus it became an auspicious and suitable move, bestowing these merits. While that cavity was burning, Ocean the lord of rivers spoke these words to Rama who knew all scientific treatises.”
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