The Khasfa sinkhole was once an inconspicuous feature in the barren desert just off the Baghdad-Mosul highway.
Now, this natural depression five miles outside Mosul is believed to be the biggest mass grave in Iraq and the resting place of an estimated 4,000 bodies.
Islamic State of Iraq and the Levant (Isil) killed and dumped the bodies of thousands of security personnel here after they captured the city in 2014, according to local villagers, Iraqi police and human rights organisations.
Most victims were shot and dumped into the pit, witnesses said, while others perished in vehicles driven over the edge.
“Daesh would drive the victims to Khasfa in convoys of minibuses, trucks and pick ups. The men had their hands bound and their eyes blindfolded.
“They were taken to the sinkhole and shot in the back of the head,” said Mahmoud, a 40-year-old from the nearby village of Sananik who declined to give his full name for security reasons.
The dead would either tumble into the hole after being shot or be tossed into it by their masked killers, he said.
The Daily Telegraph was able to visit the Khasfa site this week after Iraqi security forces fighting to recapture the western half of Mosul took control of the area.
On Friday Iraqi fighters recaptured the city’s airport from Isil, as they pushed into the densely-populated western sector.
Iraqi fighter jets also dropped bombs on Isil positions inside Syria yesterday, the first time the Iraqi government has publicly acknowledged striking militant targets inside Syria.
Isil is believed to have embarked on a campaign of extermination in Mosul, hunting down and killing policemen and soldiers and burying them in mass graves in the surrounding desert, which is pockmarked with sinkholes and natural crevices.