Experts in Israel have discovered carved hand images on the stone walls of a 10-meter-wide moat, built in the 10th century to keep enemies out.

Archaeologists recently discovered a mysterious handprint carved on the wall of a moat in the Old City of Jerusalem, as reported by Live Science on January 26. The discovery was made during a survey before an infrastructure project, where they uncovered a moat running under a busy street. According to the Israel Antiquities Authority (IAA), the moat was most likely constructed by Muslims around the 10th century to protect the city.

The moat, which is hewn from rock and measures at least 10 meters wide and 2-7 meters deep, was built to prevent enemies from approaching Jerusalem’s walls and entering the city. However, the purpose of the handprints carved on the wall remains unknown to archaeologists.

Typically, moats are filled with water, as seen in the moats surrounding castles in Europe. However, the newly excavated moat was left to dry in the hope that its massive size would be an extremely difficult obstacle for the enemy, according to Amit Re’em, an archaeologist at IAA and a member of the excavation team.

Historians of the time note that the large moat helped thwart invading forces such as the Crusaders, who besieged and attacked the city during the Siege of Jerusalem in 1099. However, the army was still able to infiltrate the city.

“Weary from the journey, the Crusaders faced the huge moat. After five weeks, they overcame it by deploying tactics and at the cost of much blood and sacrifice, under fierce fire from the Muslim and Jewish defenders,” said Re’em.

The handprint is the most intriguing element that the team of experts discovered, but it is not clear what it represents. The fingerprints may have been carved by a Muslim or Jew defending the city, or by invading European soldiers. However, it’s also possible that the meticulously carved hand represents nothing more than a joke. Researchers say that the meaning of the mysterious handprint could be revealed after further study of the dry moat is completed.