More than 1,500 years ago, an ancient Arab people built a Christian church in the Negev desert. You might know of the Nabataean civilization from its fabulous city hewn from sandstone in Petra, Jordan. The ancient Nabataeans were also formidable traders, trekking the deserts of the Arabian and Sinai peninsulas to deliver, among other goods, aromatic frankincense prized for its use in religious ceremonies. The rest of this long-abandoned oasis city, called Mamshit, has crumbled to its foundations, and the Nabataeans long since vanished as a distinct people. So I was surprised at how intact the baptismal pools were, despite the punishing heat and sand of the Negev.