Dr Andrew Petersen first became aware of a possible settlement after finding masonry and pottery at Ras Al-Sharig in Qatar.
He thought something might be there after reading sources naming a town called Rubayqa.
“But we certainly weren’t prepared for the scale of the find,” said the expert from the University of Wales, Lampeter.
The haul includes the remains of a fort, a mosque, several industrial and domestic buildings, and 100 kilos of pottery and artefacts.
Among the more unusual discoveries were Indian rupee coins set into the walls of a building believed to have been a mosque, porcelain originating from as far afield as China and Burma, and several date presses, even though dates are impossible to grow in the area.