Standing at the edge of a six-foot trench, an archaeologist from Nepal’s government peered down at a row of round holes — new evidence, he said, that below our feet lay a 2,500-year-old thatch-and-timber city where the Buddha lived until the age of 29.

The archaeologist said he was thinking about the future, when thousands of pilgrims would be climbing down from rows of buses every year to see the ruins in the Nepalese town of Tilaurakot. “We are trying to compel them to spend money here,” he said.

Similar enthusiasm could be detected about 17 miles away on the Indian side of the border, where India invites tourists to visit another site it claims are the ruins of the Buddha’s childhood home. Asked about the Nepali site, an Indian archaeologist sniffed. “The question doesn’t arise,” he said.

Begun in the glory days of the British Raj, this archaeological tug of war has remained unresolved for more than a century, of concern to virtually nobody. But changes are coming to the baking orange plains that straddle Nepal and India.

Buddhist history is an ever-more-serious business. China and India, two giants maneuvering for control in South Asia, have identified Buddhism as an instrument of soft power. In an area where, for centuries, Buddhism all but disappeared, a range of global stakeholders are investing in infrastructure to accommodate throngs of future pilgrims. India’s prize attraction is Bodh Gaya, the site where, it is believed, the Buddha attained enlightenment.

Nepal, increasingly aligned with Beijing, jealously guards its claim to the Buddha’s birth and early life.

“It is a matter of surprise that even today, in this 21st century, 2,500 years later than the time of Buddha’s birth, that it’s still a little bit confused,” said the Nepali prime minister, K. P. Sharma Oli, at a government-sponsored Buddhist conference in Kathmandu last month.

Of the conference’s 385 delegates, more than 300 were Chinese; India’s delegation numbered nine. When Mr. Oli complained about outsiders trying to encroach on Nepal’s status as the Buddha’s home, it was quite clear whom he meant.

“There are people, a few people, perhaps, who are deliberately trying to create a situation of confusion,” he said.

The site in Tilaurakot, Nepal, where many in the country believe that Buddha spent his early years. Credit Roland Lin/Unesco

Buddhist lore has it that Siddhartha Gautama, the Buddha, grew up within the luxurious setting of his father’s palace in the city of Kapilavastu, carefully guarded from any exposure to human suffering. When, at 29, Siddhartha stepped outside, he was confronted with the sight of the aged, the diseased and the dead, an experience that shook him so powerfully that he left his father’s home the following day, embracing life as an ascetic.

Until the time of the British Raj, there was little serious effort to determine where these events occurred. A powerful Hindu revival had rolled over the plains, extinguishing virtually all trace of the religion that had begun there. Then came the European Indologists, armed with the only shreds of evidence available: the accounts of Chinese monks who traveled the Buddha’s path in the fifth and seventh centuries A.D.

By the time the British withdrew, digs at two different locations had both declared victory. The modern border between Nepal and India had also come into existence, and the two claims, supported by fragmentary evidence and fired by nationalism, hardened into a cranky rivalry.

“Engulfed in complete darkness, the scholars made a beginning in the direction of locating Kapilavastu like a wild-goose chase,” K. M. Srivastava, of the Archaeological Survey of India, wrote in a memoir of his expedition to the Indian town of Piprahwa.

His discoveries, he wrote, a bit huffily, so infuriated a “particular set of scholars” that they “derived pleasure in indulging in the most unparliamentary language” questioning the identity of Kapilavastu.

The Indian consensus has held — at least in India, where tour operators market Piprahwa as “the place where the Buddha spent his childhood grappling with the overwhelming and puzzling problem of human existence.” This spring, India’s minister of culture opened a museum there, displaying evidence, mostly in the form of inscriptions on ancient seals, that was said to prove it was the true site of the Buddha’s childhood home.

Across the border in Tilaurakot, a Nepali-British team supported by Unesco has been plowing ahead with its own hypothesis: that an Indian-organized expedition in the late 1960s had simply stopped digging too early.

The leader of that Indian expedition, Debala Mitra, uncovered traces of a sprawling brick city, but she said it could not have been Kapilavastu because it had been built hundreds of years after the Buddha’s life. Last year, the Unesco-backed team cut down through the brick structures Ms. Mitra had found and discovered a second fortification whose ramparts were made of clay.

Then they dug even farther, slowing their work to a crawl. They were watching for cylindrical depressions in the earth: evidence that under the clay fort had once stood timber fence posts, perhaps for so long that the wood had decayed, leaving a shell of earth behind.

Six feet below the earth’s surface, they found them. The traces of hardened earth inside those holes, when analyzed in a laboratory, dated from the sixth century B.C., meaning they would have stood during the Buddha’s lifetime.

In late April, a scorching heat settled on the plains, and workmen used wheelbarrows to refill trenches, shutting down the expedition for the hot season. Placards were erected, announcing that “it would have been on this roadway that Siddhartha traveled on toward the Eastern Gate before renouncing his princely life.” A wooden walkway was also built so that pilgrims who prostrated themselves would not become covered in mud.

It was a bit hard to imagine a crowd there; the forest was empty except for a young boy, who was amusing himself by throwing stones. But Ram Bahadur Kunwar, from the Nepalese Department of Archaeology, paced the site of a central walled complex and spoke of great hopes.

“It is still a mystery, because we have not opened it up,” he said. “But when we do, I think that this structure will tell the history of Kapilavastu.”

Others share his excitement. The Asian Development Bank is helping to finance a $54 million upgrade of the international airport close to the Nepalese town of Lumbini, the Buddha’s birthplace. The upgraded airport, when it is completed in 2030, will accommodate 760,000 passengers a year. Lumbini is about 16 miles from Tilaurakot.

It seems that many of those visitors are expected to come from China, which is experiencing a Buddhist revival: Tour guides are picking up Mandarin, new hotels are hiring Chinese chefs, and the local authorities are planning to erect a statue of the ninth-century Chinese Buddhist pilgrim whose travel journal established Nepal as the Buddha’s birthplace. On a recent afternoon, a gaggle of women from Chengdu were clambering back onto a plane after meditating for five minutes under the branches of a tree near the Buddha’s birthplace.

Sunanda Sakyaputra, a Buddhist monk who had traveled to Tilaurakot to meditate, said the site of the ruined palace, a place where the Buddha “was not happy,” gave him a profound sense of the futility of human suffering. Asked about the town on the Indian side, he snorted.

“That is wrong, very wrong,” he said. “All things. India thinks all things are hers. Why?”