TOPSHOT - EDITORS NOTE: Graphic content / The Rapid Response Division of the Raqa civil defence excavate the site of a mass grave near the northern Syrian city of Raqa on February 19, 2019. - Two feet deep, underneath a plot of farmland outside Syria's Raqa, lies the oldest, largest, deadliest legacy of the Islamic State group: the massive grave of an estimated 3,500 people. First responders learned of the burial site in the al-Fukheikha agricultural suburb last month, more than a year after US-backed forces captured Raqa from IS and as they closed in on the group's final redoubt of Baghouz further south. (Photo by Fadel SENNA / AFP)