Researchers in the southern Ukrainian city of Odessa have unearthed at least 29 mass graves believed to contain victims of Joseph Stalin’s Great Purge, which found the Soviet dictator’s regime brutally quashing all political dissent, reports Radio Free Europe/Radio Liberty (RFE/RL).

As BBC News notes, exploratory work carried out ahead of planned expansion of Odessa’s airport uncovered the remains of between 5,000 and 8,000 people. Experts expect to find more bodies as excavations continue. The site—formerly a landfill—may be “one of the largest of its kind in Ukraine,” according to RFE/RFL.

Between 1936 and 1938, Stalin’s infamous secret police agency, the NKVD, waged a ruthless campaign of terror against high-ranking Communist Party officials and ordinary citizens alike. Estimates of the death toll vary, but History.com points out that at least 750,000 people were executed during the Great Purge (also known as the Great Terror). Millions more were detained in the Gulag, a vast system of forced labor and prison camps.

At the site in Odessa, Stalin’s enforcers “dug out pits in the garbage and threw these people in or shot them dead as they were standing there,” archaeologist Tetyana Samoylova tells Agence France-Presse (AFP). “And then they covered them with the same garbage.”

Identifying the remains may prove impossible, as official records from that period are classified and held in Moscow.

“These documents will never be handed over to us under the current government in Russia,” says Sergiy Gutsalyuk, head of the local branch of the Ukrainian Institute of National Memory (UINP), in a separate AFP report.

Per BBC News, the Soviet secret police sentenced around 8,600 people in Odessa to death between 1938 and 1941 alone. The devastation wrought by the Great Purge followed close on the heels of another atrocity: the Holodomor, a humanmade famine that killed an estimated 3.9 million Ukrainians between 1932 and 1933.

“[U]nlike other famines in history caused by blight or drought, this [one happened] when a dictator wanted both to replace Ukraine’s small farms with state-run collectives and punish independence-minded Ukrainians who posed a threat to his totalitarian authority,” wrote Patrick J. Kiger for History.com in 2019.

Per a UINP statement, archival research conducted by Odessa-based historian Aleksander Babich suggests the newly discovered burials extend beyond the landfill to an area owned by a military unit. Other mass graves have been found in the region previously: Between 1937 and 1941, for instance, Stalin’s secret police buried tens of thousands in Bykivnia, a village on the outskirts of Kiev. The mass grave’s existence was denied by authorities until the 1990s, when Ukraine built a memorial at the site. In 2007, officials reburied 1,998 of the victims interred at Bykivnia in a “somber” ceremony, as Reuters reported at the time.

“When we carry out the exhumation, we will decide what to do here,” Odessa’s mayor, Gennady Trukhanov, tells AFP. “And, of course, we plan to make a memorial.”