During the Cold War era, the United States’ Corona spy satellites snapped stealthy images of the Soviet Union, China and their allies in Southeast Asia and the Middle East. When these images were declassified in the 1990s, photos of a rocky terrace in Iraqi Kurdistan caught the attention of archaeologists, who believed they could spot the ancient remnants of a large, square fort. More recently, as Jack Malvern reports for the Times, researchers used drone technology to confirm that the site is indeed home to a previously unexplored fortified settlement.

Qalatga Darband, as the settlement is called, is located at a strategic point on the Darband-i-Rania pass, which once linked Mesopotamia to Iran, according to Lauren Sigfusson of Discovery. During the reign of Saddam Hussein and the subsequent U.S. invasion of Iraq, the region was inaccessible to archaeologists. But recent improvements in security have allowed experts from the British Museum to explore the site as part of the institution’s Iraq Emergency Heritage Management and Training Scheme, which trains Iraqi participants to document and rescue archaeological sites threatened by the Islamic State.

The team’s survey began with topographic mapping and examinations of surface pottery, according to the website of the British Museum. To get an aerial view of the landscape, researchers turned to camera-equipped drones, which are increasingly being deployed during excavations because the technology is relatively cheap to operate and quickly captures detailed images of archaeological sites.

When drone images of Qalatga Darband were processed to enhance color differences, experts were able to observe subtle irregularities in crop growth—a key indicator that an ancient structure lay hidden beneath the ground.

“Where there are walls underground the wheat and barley don’t grow so well,” John MacGinnis, a lead archaeologist of the excavation project, tells Malvern. “[S]o there are color differences in the crop growth.”

The drone images helped archaeologists conclude that their suspicions about the Corona images were correct: a large, fortified structure sits in the northern part of Qalatga Darband. The team uncovered several other buildings, including what appears to be a monumental temple. The remnants of wine or oil presses were also found.

Qalatga Darband appears to have been occupied during the early Parthian period, which spanned from the first century B.C. to the first century A.D. According to Peter Dockrill of Science Alert, a coin discovered at the site depicts the Parthian king Orodes II, who ruled between 57 B.C. and 37 B.C.

The Parthians were a major power in the ancient Near East, conquering vast swaths of territory after successful campaigns against a number of powerful groups, including the Hellenistic Seleucids and the Romans. But artifacts from Qalatga Darband suggest that Greco-Roman influences were nevertheless pervasive in the region. Archaeologists have found statues of what appear to be the Greek goddess Persephone and the Greek god Adonis, along with terracotta roof tiles modeled in the Greco-Roman architectural tradition.

Excavations at Qalatga Darband are expected to continue until 2020. Archaeologists are also investigating two other nearby sites—Murad Rasu and Usu Aska—in the hopes of gaining a more robust picture of life in the region some 2,000 years ago.