There's a lot of confusion about that word. If you look at the classical texts and the Arab historical sources, Ubar refers to a region and a group of people, not to a specific town.
People always overlook that.
It's very clear on Ptolomy's second century map of the area. It was only the late Medieval version of The One Thousand and One Nights , in the fourteenth or fifteenth century, that romanticized Ubar and turned it into a city, rather than a region or a people. It was a key site with regard to the trade that was coming and going along the edge of the great Empty Quarter. And it's one of those major sites with water. My previous work had been in northern and central Arabia, so we weren't familiar with this style of pottery.