A maritime town between the rivers Anas (modern Guadiana) and Baetis (modern Guadalquivir), it was situated on the estuary of the River Luxia (modern Odiel), and on the road from the mouth of the Anas to Augusta Emerita (modern Mérida).
The city may be the site of Tartessus; it was called Onoba by the Phoenicians. The Greeks kept the name and rendered itὌνοβα. It was in the hands of the Turdetaniat the time of conquest by Rome, and before the conquest it issued silver coins with Iberian legends. It was called both Onoba Aestuaria and Onuba (used on coinage) during Roman times, or, simply, Onoba. The city was incorporated into the Roman province of Hispania Baetica. The Arabs then called it Walbah and ruled between 712-1250. It suffered substantial damage in the 1755 Lisbon earthquake.
There are still some Roman remains. The city had a mint; and many coins have been found there bearing the name of the town as Onuba. Modern inhabitants are called Onubenses in Spanish.
Mines in the countryside send copper and pyrite to the port for export. From about 1873, the most important company in the area was Rio Tinto, the British mining firm.
During World War II, the city was a hub of espionage activities led by members of the large British and German communities. German activity centered on reporting British shipping moving in and out of the Atlantic. Most famously, the city was the location where Operation Mincemeat allowed body carrying false information to wash ashore.
The body of Glyndwr Michael, the fictional "Major William Martin, Royal Marines," is buried in the San Marco section of the cemetery of Nuestra Senora under a headstone that reads "William Martin, born 29 March 1907, died 24 April 1943, beloved son of John Glyndwyr and
