Along with the etched crosses (such as the one pictured), archaeologists found a symbol carved into the cave's pillars that looks like a Roman army pennant.

The symbol means it's possible that Roman Empire soldiers hid here, Zertal said. "It's a perfect place to hold an army--a place nobody can see."

The "$64,000 question" now is why the quarry was dug 32 feet (10 meters) underground, Zertal said. Most quarries are aboveground, so workers don't have to lift heavy rocks quite as far.

But the University of North Carolina's Magness said underground quarries are not that unusual in the region. It's also not unusual, she said, for a quarry to be reused later for other purposes.