For a route of such enormous historical stature, the Grand Trunk Road makes a surprisingly modest start to its journey across the breadth of northern India, through Pakistan to the Hindu Kush.
Maps suggest that the road sprouts out of the heart of India's great eastern city, Calcutta (also known as Kolkata), not far from the banks of the mighty Hooghly River, a distributary of the Ganges.
But if you go there -- as NPR did, at the outset of our trip along this ancient highway -- the starting point is not particularly easy to find.
Residents of Calcutta love nothing better than a good debate; the city's famous for its militant left-wing political activism.
Stop in the street and ask local residents where the road begins, and they will happily launch into a lengthy argument on the subject.
We were finally directed to a large banyan tree, beside a railway crossing, where a small throng of truck drivers were sitting in the shade, drinking tea out of clay cups, and playing cards. There was a consensus among the drivers that we had found the right place -- the spot where the Grand Trunk Road began during British colonial rule when Calcutta was the imperial capital.
The original age-old trade route, overhauled in the 16th century by northern India's last Afghan ruler, "The Lion King" Sher Shah Suri, arcs across into what is now Bangladesh. The Mughals, who succeeded the Suri Empire, extended and improved the road to the west.
The purpose of NPR's journey across the subcontinent is to meet some of the multitude of young people living along the route, and to hear about the challenges and issues they face in the 21st century. More than one-sixth of the world's population lives in South Asia; roughly half of them are under the age of 25.
So, before setting off, we made a detour to Calcutta's prestigious Presidency College, where we met a small group of students.
They spoke proudly of Calcutta’s tradition for radical left-wing thought but were critical of India’s politicians, whom they regard as too old. They stressed that India is a country in which corruption is rampant.
"Sometimes you can say that youth has shunned from politics due to disgust," said Tiyasha Sengupta, 19. "But unless we participate and try to make a change how can we expect one?"
"The government is corrupted, totally. Until and unless the corruption is being kicked out from our country, there’s no future," said 19-year-old Abhir Das.
Our conversation ranged over many subjects. It touched on the so-called Maoists who are waging war against the government in large parts of rural India.
The insurgents champion the poor and dispossessed -- particularly tribal people being forced off their traditional forest land by mineral companies and other state-backed enterprises.
The students are generally sympathetic to the rebels' cause, but they strongly condemn the use of violence.
They speak warmly of the prominent role that family and faith play in Indian life, but they reject the caste system -- the Hindu social hierarchy -- and challenge the tradition of arranged marriages.
In rural India -- and in Pakistan -- women are often reluctant to speak out. But these students strongly asserted their right to speak their minds, regardless of gender.
"You should always argue," Sengupta said. "All the great men, even George Washington and Ben Franklin, argued with the British colonists and they got their country. So why not us?"
With these words ringing in our ears, we set off on the Grand Trunk Road. Leaving Calcutta, it soon turns into a majestic new highway, part of India's so-called Golden Quadrilateral, a massive government project connecting India's four biggest cities: New Delhi, Calcutta, Chennai and Mumbai.
But first we battle our way along a narrow potholed road, through a scrum of rickshaws, motorbikes, trucks, buses, mustard yellow taxis and -- as ever in India -- animals and people.