It was a chilling discovery: a mass grave of human bones - skulls smashed and scorched by fire, dog bites on a child's thigh bone, a forehead with an apparent bullet hole.
Three years after the find by workers digging up the cloisters of a 17th-century Franciscan convent, forensic experts and historians say they have solved the mystery.
They say the estimated 3,000 dead in the grave were victims of the earthquake that devastated Lisbon in 1755, and that this is the first mass grave of its kind ever found in the Portuguese capital.
"You didn't have to be a genius to work it out. The evidence is overwhelming," says Miguel Telles Antunes, curator of the Academy of Sciences Museum who coordinated the investigation. "This could only have been some singular, calamitous event."
The quake, which included a tsunami and a fire that raged for six days, was one of the deadliest catastrophes ever to hit western Europe. It is thought to have killed up to 60,000 people, and it destroyed much of the wealthy and elegant capital of a Portuguese empire stretching across Asia, Africa and Latin America.
Historians had a rough picture of what happened on Nov. 1, 1755, but detailed accounts were scarce. Now the mass grave presents a vivid and gruesome tableau of the past.
"We had clues about what occurred. Now we have the proof," Telles Antunes said.
In the morning of November 1, 1755, a large earthquake struck Lisbon - a great city legendary for its wealth, prosperity and supposed sophistication. It was Sunday and Catholic holiday of All Saints. Most of Lisbon's population of 250,000 were praying in six cathedrals, including the Basilica de Sao Vincente de Fora. Within minutes, this great thriving city-port of Lisbon, capital of Portugal and of the vast Portuguese empire and seat of learning in Europe, was reduced to rubble by the two major shocks of this great earthquake and the waves of the subsequent catastrophic tsunami. A huge fire completed the destruction of the great city.