Valmiki describes the construction of Ram Sethu in great detail. Here is an excerpt and text (translation) of the entire sarga (Book VI: Yuddha Kanda, Book of War, Chapter [sarga] 22) where this description occurs in Valmiki Ramayana.
The architect who led the construction was Nala. This was also confirmed by Veda Vyasa in Mahabharata.
Veda Vyasa refers to the Sethu as Nalasetu (Mahabharata: 3.267.45)
?which even today, popular on earth as Nala'sbridge, mountain like, is sustained out of respect for (Lord) Rama'scommand. (Nala was son of Vishwakarma).
When Rama is about to release a missile presided over by Brahma from His bow, the sea-god appears in person before Him with joined palms and advises Him to get a bridge constructed by Nala across the ocean. The ocean god disappears after giving this advice to Rama. Nala accordingly constructs a bridge across the sea with the help of other monkeys.
athovaaca raghushreSThaH saagaram daaruNam vacaH| adya tvaam shoSayiSyaami sapaataalam mahaarNava || (2-22-1)
Then, Rama spoke these harsh words to the ocean: ?O, Ocean! I will make you dry up now along with your nethermost subterranean region.?
sharanirdagdhatoyasya parishuSkasya saagara | mayaa nihatasattvasya paamsurutpadyate mahaan || (2-22-2)
?O, Ocean! A vast stretch of sand will appear, when your water gets consumed by my arrows; when you get dried up and the creatures inhabiting you get destroyed by me.?
matkaarmukanisR^iSTena sharavarSeNa saagara | param tiiram gamiSyanti padbhireva plavaN^gamaaH || (2-22-3)
?By a gush of arrows released by my bow, our monkeys can proceed to the other shore even by foot; O, Ocean!?
vichinvannaabhijaanaasi pauruSam vaapi vikramam | daavnavaalaya samtaapam matto naama gamiSyasi|| (2-22-4)
?O, Sea the abode of demons! You are not able to recognise my valor or prowess through your intelligence. You will indeed get repentance at my hands.?
braahmeNaastreNa samyojya brahmadaNDanibham sharam | samyojya dhanuSi shre SThe vicakarSa mahaabalaH || (2-22-5)
?Fixing an arrow resembling the Rod of Brahma (the creator) charged with a missile (presided over by Brahma) to his excellent bow, the exceedingly powerful Rama stretched it towards the sea.?
tasminvikR^iSTe sahasaa raaghaveNa sharaasane | rodasii sampaphaaleva parvataashca chakampire || (2-22-6)
While Rama was stretching that bow, both the heaven and earth suddenly seemed to be split asunder. Mountains also were shaken.
tamashca lokamaavavre dishashca na chakaashire | praticukshubhire caashu saraamsi saritastadaa || (2-22-7)
Darkness enveloped the world. All the quarters were obscured. Lakes and rivers were soon agitated.
tiryak ca saha nakshatraiH samgatau candrabhaaskarau | bhaaskaraamshubhiraadiiptam tamasaa ca samaavR^itam || (2-22-8) pracakaashe tadaakaashamulkaashatavidiipitam| antarikshaachcha nirghaataa nirjagmuratulasvanaaH || (2-22-9)
The moon, sun and the stars moved obliquely and though the sun'srays lighted the sky, it was enveloped by darkness and shined with a blaze of hundreds of meteors while thunders reverberated with an unparalleled sound in the sky.
vapuHprakarSeNa vavurdivyamaarutapaN^ktyaH | babhaJNja cha tadaa vR^ikshaan jaladaanudvahan muhuH ||(2-22-10)
Series of celestial winds blew in their colossal form and the winds, then sweeping away the clouds, tore up the trees again and again.
aarujamshcaiva shailaagraan shikharaaNi babhaJNja ca | divi ca sma mahaavegaaH samhataaH samahaasvanaaH || (2-22-11) mumucurvaidyutaanagniimste mahaashanayastadaa |
The wind, shattering the mountain peaks, broke off the points of the rocks. Winds of great velocity struck together in the sky and emitted flashes of radiance proceeding from lightning with a great sound and then there were great thunders.
yaani bhuutaani dR^ishyaani chukrushushcaashaneH samam || (2-22-12) adR^ishyaani ca bhuutaani mumuchurbhairavasvanam | shishyare caabhibhuutaani samtrastaamyadvijanti ca || (2-22-13) sampravivyathire caapi na ca paspandire bhayaat |
The visible creatures cried out along with the thunders. The invisible beings too gave off a terrific noise. The creatures were overpowered, frightened, agitated, lied down and also very much anguished. They did not move due to fear.
sahabhuutaiH satoyormiH sanaagaH saharaakshasaH || (2-22-14) sahasaabhuuttato vegaadbhiimavego mahodadhiH | yojanam vyaticakraama velaamanyatra samplavaat || (2-22-15)
The great ocean with its waves and water, along with its living creatures including snakes and demons soon became possessed of a terrific velocity. Due to that speed and swelling of waters, the ocean crossed beyond the other shore to the extent of a yojan (eight miles).
tam tathaa samatikraantam naaticakraama raaghavaH | samuddhatamamitraghno raamo nadanadiipatim || (2-22-16)
Rama born in Raghu dynasty and the annihilator of enemies, did not retreat before that ocean, which swelled and crossed its limits.
tato madhyaat samudrasya saagaraH svayam utthitaH | udayan hi mahaashailaan meror iva divaa karaH || (2-22-17)
Then, Sagara (the ocean god) himself rose from the middle of the ocean as the sun rises at dawn from the huge mountain of Meru.
pannagaiH saha diipta aasyaiH samudraH pratyadR^ishyata| snigdha vaiduurya samkaasho jaambuu nada vibhuuSitaH || (2-22-18)
That ocean along with snakes of flaming jaws appeared with a hue of glossy emerald adorned with gold.
ratna maalya ambara dharaH padma patra nibha iikSaNaH| sarvapuSpamayiim divyaam shirasaa dhaarayan srajam || (2-22-19)
jaataruupamayaishcaiva tapaniiyavibhuuSito bhuuSaNottamaiH| aatmajaanaam ca ratnaanaam bhuuSito bhuuSaNottamaiH || (2-22-20)
dhaatubhirmaNDitaH shailo vividhairhamavaaniva | ekaavaliimadhyagatam taralam paaNDaraprabham || (2-22-21)
vipulenorasaa bibhratkaustubhasya sahodaram | aaghuurNitataraN^-gaughaHkaalikaanilasamkulaH || (2-22-22) gaN^gaasindhupradhaa-naabhiraapagaabhiH samaavR^itaH|
devataanaam saruupaabhirnaa-naaruupaabhiriishvaraH|| (2-22-23) saagaraH samatikramya puurvam aamantrya viiryavaan | abraviit praanjalir vaakyam raaghavam shara paaNinam || (2-22-24)
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:
pR^ithivii vaayur aakaasham aapo jyotiH ca raaghavaH | svabhaave saumya tiSThanti shaashvatam maargam aashritaaH || (2-22-25)
?O, beloved Rama! Earth, wind ether, water and light remain fixed in their own nature, resorting to their eternal path.?
tat svabhaavo mama api eSa yad agaadho aham aplavaH | vikaaras tu bhaved raadha etat te pravadaami aham || (2-22-26)
?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.?
na kaamaan na ca lobhaad vaa na bhayaat paarthiva aatmaja| raagaannakraakulajalam stambhayeyam kathamcana || (2-22-27)
?O, Prince! Neither from desire nor ambition nor fear nor from affection, I am able to solidify my waters inhabited by alligators.?
vidhaasye yena gantaasi viSahiSye hyaham tathaa | na graahaa vidhamiSyanti yaavatsenaa tariSyati|| (2-22-28) hariiNaam taraNe raama kariSyaami yathaasthalam |
?O, Rama! 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.?
tamabraviittadaa raamaH shR^iNu me varuNaalaya || (2-22-29) amogho.ayam mahaabaaNaH kasmin deshe nipaatyataam |
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??
raamasya vachanam shrutvaa tam ca dR^iSTvaa mahaasharam|| (2-22-30) mahodadhirmahaatejaa raaghavam vaakyamabraviit |
Hearing Rama'swords and seeing that powerful arrow, the large splendid Ocean spoke the following words to Rama:
uttareNaavakaasho.asti kashchitpuNyataro mama || (2-22-31) drumakulya iti khyaato loke khyaato yathaa bhavaan |
?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.?
Hearing those words of the high-soled ocean, Rama released that excellent and splendid arrow towards that place as directed by the ocean.
tena tanmarukaantaaram p^ithivyaam kila vishrutam || (2-22-35) vipaatitaH sharo yatra vajraashanisamaprabhaH|
The place where the arrow, whose splendor was akin to that of a thunder and a thunderbolt, was descended by Rama- that place is indeed famous as desert of Maru* on this earth. (*Maru is Malwar in Rajasthan, India)
nanaada ca tadaa tatra vasudhaa shalyapiiDitaa || (2-22-36) tasmaadbaaNamukhaattoyamutpapaata rasaatalaat |
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.
sa babhuuva tadaa kuupo vraNa ityeva vishrutaH || (2-22-37) satatam cotthitam toyam samudrasyeva dR^ishyate |
Then the hollow became known as Vrana. Water constantly seen, gushing forth from it resembled seawater.
avadaaraNashabdashca daaruNaH samapadyata || (2-22-38) tasmaattadbaaNapaatena apaH kukshiSvashoSayat |
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.
vikhyaatam triSu lokeSu madhukaantaarameva ca || (2-22-39) shoSayitvaa tu tam kukshim raamo dasharathaatmajaH | varam tasmai dadau vidvaanmarave.-amaravikramaH || (2-22-40)
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.
pashavyashcaalparogashca phalamuularasaayutaH | bahusneho bahukshiiraH sugandhirvivi-dhauSadhiH || (2-22-41) evametairguNairyukto bahibhiH samyuto maruH | raamasya varadaanaacca shivaH panthaa babhuuva ha || (2-22-42)
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.
tasmin dagdhe tadaa kukshau samudraH saritaam patiH | raaghavam sarvashaas-trajJNamidam vacanambraviit || (2-22-43)
While that cavity was burning, ocean, the lord of rivers, spoke these words to Rama who knew all scientific treatises.
ayam saumya nalo naama tanujo vishva karmaNaH | pitraa datta varaH shriimaan pratimo vishva karmaNaH || (2-22-44)
?O, Excellent man! This one, named Nala, a glorious person, is the son of Vishvakarma; who was given a boon by his father and is equal to Vishvakarma.?
eSa setum mahaautsaahaH karotu mayi vaanaraH | tam aham dhaarayiSyaami tathaa hi eSa yathaa pitaa || (2-22-45)
?Let this greatly energetic monkey build a bridge across me. I can hold that bridge. He is just the same as his father.?
evam uktvaa udadhir naSTaH samutthaaya nalas tataH | abraviid vaanara shreSTho vaakyam raamam mahaabalaH || (2-22-46)
Thus speaking, the god of ocean disappeared from that place. Then Nala, the more distinguished among monkeys stood up and spoke the following words to Rama of great power:
aham setum kariSyaami vistiirNe varuNa aalaye | pituH saamarthyam aasthaaya tattvam aaha mahaaudadhiH|| (2-22-47)
?The great ocean disclosed a truth. I will construct a bridge across this large ocean, taking recourse to the skill and ability of my father.?
asau tu saagaro bhiimaH setukarmadidR^ikshayaa | dadau daNDabhayaadgaadham raaghavaaya mahodadhiH || (2-22-48)
?This Sagara, the formidable mass of water, in fear of punishment, gave a passage to Rama, wishing to see a bridge constructed on it.?
mama maatur varo datto mandare vishva karmaNaa | aurasas tasya putro aham sadR^isho vishva karmaNaa || (2-22-49)
?On the mountain of Mandara, the following boon was given by Vishvakarma to my mother: ?O, god like lady! A son equal to me will be born to you.?
aurasastasya putro.aham sadR^isho vishvakarmaNaa| smaarito.asmyahametena tattvamaaha mahodadhiH || (2-22-50) na ca api aham anukto vai prabruuyaam aatmano guNaan|
?I am a son born of Vishvakarma'sown loins. I am equal to Vishvakarma. This god of ocean has reminded me. The great ocean spoke the truth. Being unasked, I have not told you my details earlier.?
samarthshcaapyaham setum kartum vai varuNaalaye || (2-22-51) tasmaadadyaiva badhnantu setum vaanarapuN^gavaaH |
?I am capable of constructing a bridge across the ocean. Hence, let the foremost of monkeys build the bridge now itself.?
tato nisR^iSTa raameNa sarvato hari yuuthapaaH || (2-22-52) abhipetur mahaaaraNyam hR^iSTaaH shata sahasrashaH |
Then, being sent by Rama, hundreds and thousands of monkey heroes jumped in joy on all sides towards the great forest.
te nagaan naga samkaashaaH shaakhaa mR^iga gaNa R^iSabhaaH|| (2-22-53) babhanjur vaanaraas tatra pracakarSuH ca saagaram |
Those army-chiefs of monkeys, who resembled mountains, broke the rocks and trees there and dragged them away towards the sea.
te saalaiH ca ashva karNaiH ca dhavair vamshaiH ca vaanaraaH|| (2-22-54) kuTajair arjunais taalais tikalais timishair api | bilvakaiH saptaparNaishca karNikaaraishca puSpitaiH || (2-22-55) cuutaiH ca ashoka vR^ikSaiH ca saagaram samapuurayan |
Those monkeys filled the ocean with all types of trees like Sala and Asvakarna, Dhava and bamboo, Kutaja, Arjuna, palmyra,Tilaka, Tinisa, Bilva, Saptaparna, Karnika, in blossom as also mango and Asoka.
samuulaamH ca vimuulaamH ca paadapaan hari sattamaaH|| (2-22-56) indra ketuun iva udyamya prajahrur harayas taruun |
The excellent monkeys, the forest animals lifted and brought, like Indra'sflag posts, some trees with roots intact and some others without roots.
taalaan daaDimagulmaamshca naarikelavibhiitakaan || (2-22-57) kariiraan bakulaannimbaan samaajahruritastataH |
From here and there the monkeys brought Palmyra trees, pomegranate shrubs, coconut and Vibhitaka, Karira, Bakula and neem trees.
hastimaatraan mahaakaayaaH paaSaaNaamshca mahaabalaaH || (2-22-58) parvataamshca samutpaaTya yantraiH parivahanti ca |
The huge bodied monkeys with mighty strength uprooted elephant-sized rocks and mountains and transported them by mechanical contrivances.
prakSipyamaaNair acalaiH sahasaa jalam uddhatam || (2-22-59) samutpatitam aakaasham apaasarpat tatas tataH |
The water, raised up due to sudden throwing of mountains in the sea, soured upward towards the sky and from there again, gushed back.
samudram kshobhayaa-maasurnipatantaH samantataH || (2-22-60) suutraaNyanye pragR^ihNanti hyaayatam shatayojanam |
The rocks befalling on all sides perturbed the ocean. Some others drew up strings a hundred yojans long (in order to keep the rocks in a straight line.)
nalaH cakre mahaasetum madhye nada nadii pateH || (2-22-61) sa tadaa kriyate seturvaanarai rghorakarmabhiH |
Nala on his part initiated a monumental bridge in the middle of the ocean. The bridge was built at that time with the cooperation of other monkeys, of terrible doings.
daNDananye pragR^ihNanti vicinvanti tathaapare || (2-22-62) vaanaraiH shatashastatra raamasyajJNaapuraHsaraiH | meghaabhaiH parvataabhashca tR^iNaiH kaaSThairbabandhare || (2-22-63)
Some monkeys were holding poles for measuring the bridge and some others collected the material. Reeds and logs resembling clouds and mountains, brought by hundreds of monkeys, lead by the command of Rama, fastened some parts of the bridge.
puSpitaagraishcha tarubhiH setum badhnanti vaanaraaH | paaSaaNaamshca giriprakhyaan giriiNaam shikharaaNi ca || (2-22-64) dR^ishyante paridhaavanto gR^ihya daanavasamnibhaaH |
Monkeys constructed the bridge with trees having blossom at the end of their boughs. Some monkeys looking like demons seized rocks resembling mountains and peaks of mountains and appeared running hither and thither.
shilaanaam kSipyamaaNaanaam shailaanaam tatra paatyataam || (2-22-65) babhuuva tumulaH shabdas tadaa tasmin mahaaudadhau |
Then, a tumultuous sound occurred when the rocks were thrown into the sea and when mountains were caused to fall there.
kR^itaani prathamenaahnaa yojanaani caturdasha || (2-22-66) prahR^iSTaijasamkaashaistvaramaaNaiH plavaN^gamaiH |
On the first day, fourteen yojans of bridge was constructed by the monkeys speedily, thrilled with delight as they were, resembling elephants.
dvitiiyena tathaivaahnaa yojanaani tu vishatiH || (2-22-67) kR^itaani plavagaistuurNam bhiimakaayairmahaabalaiH |
In the same manner, on the second day twenty yojans of bridge was constructed speedily by the monkeys of terrific bodies and of mighty strength.
ahnaa tR^itiiyena tathaa yojanaani tu saagare || (2-22-68) tvaramaaNairmahaakayaireka-vimshatireva ca |
Thus, on the third day twenty-one yojans of the bridge was constructed in the ocean speedily by the monkeys with their colossal bodies.
caturthena tathaa caahnaa dvaavimshatirathaapi vaa || (2-22-69) yojanaani mahaavegaiH kR^itaani tvaritaistataH |
On the forth day, a further of twenty-two yojans was constructed by the dashing monkeys with a great speed.
paJNcamena tathaa caahnaa plavagaiH kshiprakaaribhiH || (2-22-70) yojanaani trayovimshat-suvelamadhikR^itya vai|
In that manner, on the fifth day, the monkeys working quickly constructed twenty-three yojans of the bridge up to the other seashore.
sa vaanaravaraH shriimaan vishvakarmaatmajo balii || (2-22-71) babandha saagare setum yathaa caasya tathaa pitaa |
That Nala, the strong and illustrious son of Vishvakarma and an excellent monkey built the bridge across the sea as truly as his father would have built it.
sa nalena kR^itaH setuH saagare makara aalaye || (2-22-72) shushubhe subhagaH shriimaan svaatii patha iva ambare |
That beautiful and lovely bridge constructed by Nala across the ocean the abode of alligators, shone brightly like a milky way of stars in the sky.
tato devaaH sagandharvaaH siddhaaH ca parama R^iSayaH || (2-22-73) aagamya gagane tasthurdraSTu-kaamaastadadbhutam|
With a desire to behold that marvel, celestials along with Gandharvas, the heavenly musicians, Siddhas (semi-divine beings of great purity and perfection, possessing super natural qualities) and great sages came then and stood up in the sky.
That colossal bridge, which was broad, well-constructed, glorious, well postured and held together firmly, looked beautiful like a separating straight line in the ocean.
Vibhishana, wielding a mace in his hand, stood up on the seashore along with his ministers, for the purpose of invading the enemies.
sugriivastu tataH praaha raamam satyaparaakramam | hanumantam tvamaaroha aN^gadam tvatha lakshmaNaH || (2-22-80) ayam hi vipulo viira saagaro makaraalayaH| vaihaayasau yuvaametau vaanarau dhaarayiSyataH|| (2-22-81)
Thereafter, Sugriva on his part spoke to Rama, the truly brave man as follows: ?O, Valiant man! This ocean, the abode of alligators, is indeed vast. You ascend the shoulder of Hanuman and let Lakshmana ascend the shoulder of Angada. These monkeys can hold both of you while flying in the sky.?
agratas tasya sainyasya shriimaan raamaH salakshmaNaH| jagaama dhanvii dharma aatmaa sugriiveNa samanvitaH || (2-22-82)
Rama the glorious and righteous man, wielding a bow along with Lakshmana together with Sugriva, went in front of that army.
Seeing that Rama'saccomplishment, which was amazing and arduous; celestials, Siddhas (semi-divine beings possessing supernatural faculties) and Charanas (celestial bards) along with great sages, forthwith approached Rama and consecrated him with very splendid waters separately.
jayasva shatruun nara deva mediniim | sasaagaraam paalaya shaashvatiiH samaaH | iti iva raamam nara deva satkR^itam| shubhair vacobhir vividhair apuujayan || (2-22-87)
The celestials, Siddhas and others exalted Rama, who was duly respected by kings with their auspicious words as follows: ? O, king! Defeat the enemies. Rule the earth and ocean eternally for years.?
Thus completes 22nd Chapter of Yuddha Kanda of the glorious Ramayana of Valmiki, the work of a sage and the oldest epic.