Nala, chief Vanara engineer of Sethu (Bridge) between Rameswaram and Lanka, used trees and rocks cut by machines, but not floating stones with name of Rama written on them.
Valmiki Ramayana clearly mentions in Yuddha Kanda, 22nd Sarga about how Nala planned the construction of bridge till Lanka.
Other Ramayana versions or translations written in other languages might have spread that stones floated as Rama’s name was written on them.
Few tour guides near Rameswaram, even cheated tourists by showing floating stones in water.
This bridge, infact should be called as Nala Sethu or Nala’s Bridge, but not Rama Sethu, as it was completely Nala’s idea.
Valmiki calls it Nala Setu, so also Vyasa in the Mahabharata calls it Nala Setu.
Valmiki wrote that Nala erected the Setu using trees, which were brought by Vanara army. Valmiki never says that the rocks floated on water. On the contrary he states that big rocks were cut with machines and thrown in to the sea, which sank and on that foundation, a Setu (bridge) of wood was built.
Valmiki wrote a true history, but later it was distorted by devotional writings Tulasidas Ram Charit Manas etc.
At the point where bridge began, Sea was shallow. So, boats could not pass through those waters.
Nala intelligently filled up the gaps in that row, with wood and made a temporary bridge. After many years, wood will be washed away and rocks will remain underneath.
विधास्ये येन गन्तासि विषहिष्ये ह्यहम् तथा |
न ग्राहा विधमिष्यन्ति यावत्सेना तरिष्यति || २-२२-२८
हरीणाम् तरणे राम करिष्यामि यथास्थलम् |
Translation : 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.
ते नगान् नग सम्काशाः शाखा मृग गण ऋषभाः || २-२२-५३
बभन्जुर् वानरास् तत्र प्रचकर्षुः च सागरम् |
Translation : Those army-chiefs of monkeys, who resembled mountains, broke the rocks and trees there and dragged them away towards the sea.
ते सालैः च अश्व कर्णैः च धवैर् वंशैः च वानराः || २-२२-५४
कुटजैर् अर्जुनैस् तालैस् तिकलैस् तिमिशैर् अपि |
बिल्वकैः सप्तपर्णैश्च कर्णिकारैश्च पुष्पितैः || २-२२-५५
चूतैः च अशोक वृक्षैः च सागरम् समपूरयन् |
Translation : 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.
समूलामः च विमूलामः च पादपान् हरि सत्तमाः || २-२२-५६
इन्द्र केतून् इव उद्यम्य प्रजह्रुर् हरयस् तरून् |
Translation : The excellent monkeys, the forest animals lifted and brought, like Indra’s flag posts, some trees with roots intact and some others without roots.
तालान् दाडिमगुल्मांश्च नारिकेलविभीतकान् || २-२२-५७
करीरान् बकुलान्निम्बान् समाजह्रुरितस्ततः |
Translation : From here and there the monkeys brought Palmyra trees, pomegranate shrubs, coconut and Vibhitaka, Karira, Bakula and neem trees.
हस्तिमात्रान् महाकायाः पाषाणांश्च महाबलाः || २-२२-५८
पर्वतांश्च समुत्पाट्य यन्त्रैः परिवहन्ति च |
Translation : The huge bodied monkeys with mighty strength uprooted elephant-sized rocks and mountains and transported them by machines.
प्रक्षिप्यमाणैर् अचलैः सहसा जलम् उद्धतम् || २-२२-५९
समुत्पतितम् आकाशम् अपासर्पत् ततस् ततः |
Translation : The water, raised up due to sudden throwing of mountains in the sea, soured upward towards the sky and from there again, gushed back.
समुद्रम् क्षोभयामासुर्निपतन्तः समन्ततः || २-२२-६०
सूत्राण्यन्ये प्रगृह्णन्ति ह्यायतम् शतयोजनम् |
Translation : The rocks befalling on all sides perturbed the ocean. Some others drew up strings a hundred Yojanas long (in order to keep the rocks in a straight line.
नलः चक्रे महासेतुम् मध्ये नद नदी पतेः || २-२२-६१
स तदा क्रियते सेतुर्वानरै र्घोरकर्मभिः |
Translation : 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.
दण्डनन्ये प्रगृह्णन्ति विचिन्वन्ति तथापरे || २-२२-६२
वानरैः शतशस्तत्र रामस्यज्ञापुरःसरैः |
मेघाभैः पर्वताभश्च तृणैः काष्ठैर्बबन्धरे || २-२२-६३
Translation : 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.
पुष्पिताग्रैश्च तरुभिः सेतुम् बध्नन्ति वानराः |
पाषाणांश्च गिरिप्रख्यान् गिरीणाम् शिखराणि च || २-२२-६४
दृश्यन्ते परिधावन्तो गृह्य दानवसम्निभाः |
Translation : 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.
शिलानाम् क्षिप्यमाणानाम् शैलानाम् तत्र पात्यताम् || २-२२-६५
बभूव तुमुलः शब्दस् तदा तस्मिन् महाउदधौ |
Translation : Then, a tumultuous sound occurred when the rocks were thrown into the sea and when mountains were caused to fall there.
कृतानि प्रथमेनाह्ना योजनानि चतुर्दश || २-२२-६६
प्रहृष्टैजसम्काशैस्त्वरमाणैः प्लवङ्गमैः |
Translation : On the first day, fourteen Yojanas of bridge were constructed by the monkeys speedily, thrilled with delight as they were, resembling elephants.
द्वितीयेन तथैवाह्ना योजनानि तु विशतिः || २-२२-६७
कृतानि प्लवगैस्तूर्णम् भीमकायैर्महाबलैः |
Translation : In the same manner, on the second day twenty Yojanas of bridge were constructed speedily by the monkeys of terrific bodies and of mighty strength.
अह्ना तृतीयेन तथा योजनानि तु सागरे || २-२२-६८
त्वरमाणैर्महाकयैरेकविंशतिरेव च |
Translation : Thus, on the third day twenty-one Yojanas of the bridge were constructed in the ocean speedily by the monkeys with their colossal bodies.
चतुर्थेन तथा चाह्ना द्वाविंशतिरथापि वा || २-२२-६९
योजनानि महावेगैः कृतानि त्वरितैस्ततः |
Translation : On the fourth day, a further of twenty-two Yojanas were constructed by the dashing monkeys with a great speed.
पञ्चमेन तथा चाह्ना प्लवगैः क्षिप्रकारिभिः || २-२२-७०
योजनानि त्रयोविंशत्सुवेलमधिकृत्य वै |
Translation : In that manner, on the fifth day, the monkeys working quickly constructed twenty-three yojanas of the bridge up to the other seashore.
विशालः सुकृतः श्रीमान् सुभूमिः सुसमाहितः |
अशोभत महासेतुः सीमन्त इव सागरे || २-२२-७८
Translation : 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.