A huge man-made cave was discovered in the Jordan valley of Isreal that's 2,000 years old and supposedly the largest of all at an acre (.4 hectare) in area coverage. Inside, archaeologists like Adam Zertal, have found deep etchings on walls and pillars of what used to be an underground quarry. The researchers pointed to crosses (top) and symbols that Zertal had identified as a possible zodiac symbol (above left) used in the Roman era at around 1 A.D.
The cave was found in March, 2009 when the archaeologists came to a hole in the wall of the ancient quarry. Initial forays already revealed a huge pillared chamber, discernible even with little available light. The cave is believed to have been used as a hideout of persecuted Christians and as a refuge for Roman soldiers. It's also possible that it was used as a monastery, although only the etched crosses serve as a basis for this hypothesis.