While they can date it all, they don't know why these ships were drawn in the middle of a desert.
Dr. Davida Eisenberg-Degen, rock-art expert at the Israel Antiquities Authority, dated the cistern to around the 1st or 2nd century, based on the methods used to carve the staircase out of the bedrock and the plastering over the steps, both of which are indicative of the Ancient Roman style.
Eisenberg-Degen theorized that the cistern provided water for near by housing and was in use as recently as World War I. After WWI, however, the cistern seems to have been lost to memory. It was only re-discovered during an archaeological survey of the area, which the city of Be’er Sheva planned to develop.
The cistern is quite large: 5 meters by 5.5 meters, and 12 meters deep. Desert cisterns are usually built big in order to save every drop of water possible, especially in the Negev region, which sees only about 200 mm of rain annually.
Inside the cistern, the team found 13 different images of boats drawn on the walls. Each one was found to have the appropriate proportions and showed evidence that the artist had the technical know-how to build ships. Eisenberg-Degen explained:
“The details are strikingly accurate,” Eisenberg-Degen said. “For instance, the mast is drawn going to the floor of the boat, shows understanding of shipbuilding technique. Ropes are shown near the mast and further away, holding the mast in place, all technical details that show understanding. I wouldn’t have considered that the mast needs to go down to the ship’s base if I didn’t know boat construction.”
While it is unclear exactly when the cistern went into disuse, they theorize that it was after WWI, since they found artifacts from that era in the silt at the bottom, including pottery bits, ammunition shells and weapon parts from WWI era firearms.
It is also unknown why these ships were drawn inside a cistern in the middle of a desert. One might expect to find images of ships or schematics drawn in a port city, but nearly 40 miles away from the Mediterranean Sea, no ships would have been built. Perhaps it was just for decoration — and after a particularly heavy rain the water would rise high enough to make the ships look as though they were sailing.