DALLAS - A stone tablet thought to be about 1,500 years old with a worn-down chiseled inscription of the Ten Commandments will be sold next month at auction, with a stipulation that the buyer must put it on public display, an auction house has said. The two-foot (61 cm) square slab of white marble weighs about 200 pounds (90kg) and is believed to be the oldest existing stone inscription of the commandments, Dallas-Based Heritage Auctions said. Opening bid is $250,000 for the stone, which the current owner likes to point out is not the original. The tablet is inscribed in Samaritan script with the principles which are fundamental to Judaism and Christianity. It was probably chiseled during the late Roman or Byzantine era, between 300 and 500 A.D., and marked the entrance of an ancient synagogue that was likely destroyed by the Romans, Heritage said in a statement.