The two archaeologists had a hunch that the Buddha's birthplace in southern Nepal held secrets that could transform how the world understood the emergence and spread of Buddhism.
Their pursuit would eventually see them excavate the sacred site of Lumbini as monks prayed nearby, leading to the stunning claim that the Buddha was born in the sixth century BC, two centuries earlier than thought.
Veteran Nepalese archaeologist Kosh Prasad Acharya had carried out excavations in Lumbini before in the early 1990s, when Nepal was still ruled by a king and a Maoist insurgency had yet to kick off.
The project ended in 1996 but Acharya remained unsatisfied with the results.
"My belief was that there was another cultural deposit below, which we had not uncovered," the 62-year-old told AFP.
He headed back to his government job in the capital Kathmandu and waited to retire, restless to return to Lumbini.
The Buddha's birthplace was lost and overgrown by jungle before its rediscovery in 1896, when the presence of a third century BC pillar bearing inscriptions allowed historians to identify it as Lumbini.
Since then, it has been designated a UNESCO world heritage site, visited by millions of Buddhists every year, with numbers expected to rise exponentially in the following decades.
Acharya had just retired from his last job, as the director general of the department of archaeology, when UNESCO asked him to co-direct an investigation of Lumbini's foundations.
The cultural organisation asked Acharya and his longtime collaborator, Robin Coningham, Britain's leading South Asian archaeologist, to head a team that would examine the site so conservators could develop it for growing numbers of visitors.
"In 2010, our first year there, we were pretty much the handmaidens to the conservators," Coningham told AFP in a phone interview from his office at Britain's Durham University, which helped fund the UNESCO project.
"The Eureka moment came in 2011, when we came across a brick temple located below the existing Asokan temple, and below that a sort of void.
"It became clear then that there was much more to this excavation."
Over the next two years, archaeologists, geophysicists and hired workmen from Nepal and Britain worked on the site, digging in the presence of meditating monks and nuns.
"It was a very moving, very special experience to dig for traces while pilgrims prayed and paid homage," Acharya said.
They dug for a few weeks each year and sent the samples to laboratories for analysis.
