Civil Engineers built Highway in Ramayana

Valmiki Ramayana describes highly skilled engineers, excavators, mechanics, carpenters, road-menders, wood-cutters, hollow-makers, men skilled in plastering and white washing, basket makers, tanners and skilled supervisors building Highway from Ayodhya to river Ganga.
Highway in Ramayana from Ayodhya to Prayaga

2nd Chapter in Ramayana, Ayodhya Kanda describes in Sarga 80, that Rama’s younger brother Bharata along with his army goes out into forest in search of his brother.
After Rama, Seetha and Lakshmana left for forest, Bharata tries to follow him, with hope of bringing his elder brother back to kingdom.
Sarga 80 describes a highway being contructed from Ayodhya till Ganga river.
Satrughna and Bharata, who were away when Rama was sent to forest, comeback to city and meet at Assembly to discus what is to be done next.
Bharata refuses to rob the throne from Rama and goes out in search of him.
He orders construction of a highway from Ayodhya city till banks of Ganga river.
After reaching the river, he meets Guha who further explains whereabouts of Rama.
Bharata and army ferry across the river by boats.

अथ भूमि प्रदेशज्ञाः सूत्र कर्म विशारदाः |
स्व कर्म अभिरताः शूराः खनका यन्त्रकाः तथा || २-८०-१
कर्म अन्तिकाः स्थपतयः पुरुषा यन्त्र कोविदाः |
तथा वर्धकयः चैव मार्गिणो वृक्ष तक्षकाः || २-८०-२
कूप काराः सुधा कारा वंश कर्म कृतः तथा |
समर्था ये च द्रष्टारः पुरतः ते प्रतस्थिरे || २-८०-३

Translation : Civil engineers who were able to advise on the nature of soils, those skilled in thread-holding for leveling purposes, those who were energetic courageous and attentive in doing their jobs, excavators, mechanics, labourers, carpenters, road-menders, wood-cutters, hollow-makers, men skilled in plastering and white washing, basket makers, tanners and skilled supervisors of work sallied forth in advance.

Those mighty assembly of men gladly setting out to that forest was splendid like an ocean on the day of the full moon having a gigantic commotion.

ते स्व वारम् समास्थाय वर्त्म कर्माणि कोविदाः |
करणैः विविध उपेतैः पुरस्तात् सम्प्रतस्थिरे || २-८०-५

Men skilled in making roads, furnished with tools of every kin, seeking the company of men of their own proper place, marched ahead. Clearing away rows of creepers and shrubs timber and big rocks as well as variours kinds of trees (which obstructed the way), they carved out a path. Some men planted trees in tree-less areas. Some others chopped the existing trees here and there by means of axes, hatchets and sickles.

अपरे वीरण स्तम्बान् बलिनो बलवत्तराः |
विधमन्ति स्म दुर्गाणि स्थलानि च ततः ततः || २-८०-८

Some other strong men removed sturdy tufts of Virana grass and leveled the uneven places here and there. Some others filled up wells and extensive pits with earth. Some men leveled low-lying places all around. Then, some men bridged the steams that could be bridged, pulverised the rocks that could be pulverised and smashed (the impediments that blocked the flow of water) those which could be smashed. Many ponds, in various sizes and shapes containing plenty of water resembling seas were built (by constructing dams on rivulets).

निर्जलेषु च देशेषु खानयामासुरुत्तमान् |
उदपानान् बहुविधान् वेदिका परिमण्डितान् || २-८०-१२

In water-scarce areas, excellent wells in various shapes were dug duly decorated all around with platforms (to rest). That track of the troops, having its surface inlaid with cement, with flowering trees inlaid with cement, with flowering trees on both sides, inhabited with birds in excitement making their sounds, adorned with flags on its either side with its surface sprinkled with water of sandal-wood fragrance, and decorated with various kinds of flowers, looked very much splendid like the path of celestials.

आज्ञाप्य अथ यथा आज्ञप्ति युक्ताः ते अधिकृता नराः |
रमणीयेषु देशेषु बहु स्वादु फलेषु च || २-८०-१५
यो निवेशः तु अभिप्रेतः भरतस्य महात्मनः |
भूयः तम् शोभयाम् आसुर् भूषाभिर् भूषण उपमम् || २-८०-१६

Those officers appointed for execution of the work, as ordered by Bharata, skillfully instructed their work-men and erected a tent which was intended for the great-souled Bharata, in a beautiful place abundant with tasty fruits. They further adorned profusely with decorations, the tent which itself resembled on ornament. The connoisseurs erected the tents of the high-souled Bharata at auspicious hours in days when the stars were propitious.

बहु पांसु चयाः च अपि परिखा परिवारिताः |
तन्त्र इन्द्र कील प्रतिमाः प्रतोली वर शोभिताः || २-८०-१८
प्रासाद माला सम्युक्ताः सौध प्राकार सम्वृताः |
पताका शोभिताः सर्वे सुनिर्मित महा पथाः || २-८०-१९
विसर्पत्भिर् इव आकाशे विटन्क अग्र विमानकैः |
समुच्च्रितैः निवेशाः ते बभुः शक्र पुर उपमाः || २-८०-२०

Those camps, with many breast works of sand, moats surrounding each of them, streets as resplendent as sapphires, their crowns of terrets, the ramparts covered with stucco to protect then, the splendid banners, the skillfully laid out avenues, lofty mansions the tops of which were provided with dove-cots, which flew about as it were in the air and in splendour, resembled the capitals of Indra.

The route thus prepared, extended up to the Ganga River, whose pure and limpid waters, abounding in great fish, flowed between woods and forests of every kind.
सचन्द्र तारा गण मण्डितम् यथा |
नभः क्षपायाम् अमलम् विराजते |
नर इन्द्र मार्गः स तथा व्यराजत |
क्रमेण रम्यः शुभ शिल्पि निर्मितः || २-८०-२२

That beautiful Royal High Way (Narendramarga), which was built gradually by efficient engineers, appeared as resplendent as a night in a clear sky, illumined by the moon with its procession of stars.