The etchings were found on the walls of an ancient limestone cistern, as Ilan Ben Zion writes:
A group of Israel Caving Club members were exploring hidden caves in the Judean lowlands . . . when they discerned the carvings: a three-footed menorah with seven branches similar to the one that stood in the Jerusalem temple, a cross, and a depiction of an ancient key. Other as-yet-unidentified carvings were also found. . . .
Sa’ar Ganor, an archaeologist with the Israel Antiquities Authority, . . . studied the engravings and determined that the menorah was likely carved sometime during the Second Temple period—about 530 BCE to 70 CE—and the cross likely in the Byzantine period, around the 4th century CE.
“It’s rare to find a wall engraving of a menorah,” which is a “distinctly Jewish symbol,” Ganor said. . . [O]nly two menorah engravings exist in the region where it was found: one in an oil press at Beit Loya and the other in a tomb near Beit Guvrin—both east of the modern city of Kiryat Gat.
Read more on Times of Israel: http://www.timesofisrael.com/hanukkah-hikers-find-rare-2nd-temple-era-etchings-of-menorah-and-cross/