Workmen digging the foundations of a new metro station in Algeria's capital stumbled on an archaeological goldmine that gives new meaning to "time travel" - opening a window on 2,300 years of history. Relics from the French colonial era lie on top of those from the Ottoman period, in turn covering those from the Middle Ages and early Roman Empire.
Then comes what archaeologists hope will be ruins from the Punic period - when Phoenician traders established north African outposts in the first millennium BC. Work on the metro station has now been stopped and archaeologists and academics have replaced labourers on the site at the far end of the Casbah, the historic heart of the capital placed on UNESCO's world heritage list in 1992.
Fences prevent entry to the area on Martyrs Square as excavations take place right next to the 12th-century grand mosque. Teams of specialist workers probe the ground under the watchful eyes of Algerian and French archaeologists. In just a few weeks, an area covering several dozen square metres has been opened up, confirming the initial findings by the city's cultural authority in 2008.
Experts initially uncovered relics from the beginning of French colonisation in the 1830s before Ottoman remains came to light. "Here's the workshop of an iron worker with its forge still visible," said Kamel Stiti, co-director of the excavations and a member of Algeria's national centre for archaeological research. "This site is evidence of a whole neighbourhood of craftsmen being here," he said.
Stiti believes the Ottoman neighbourhood was built on the ruins of the medieval city, traces of which have also been found, along with several graves and complete skeletons. Beneath that came the remains of a Paleo-Christian church dating from the 4th or 5th century AD, said Francois Souq, director for the Mediterranean region at the National Institute for Preventive Research (INRAP) in the southern French city of Nimes. The bases of columns are still visible, surrounding a nave around 20 metres (65 feet) wide, with the floor covered in mosaics.
The archaeologists hope that by digging a bit deeper they will uncover remains dating from the Punic era, when the Phoenicians built trading posts along a 1,200-kilometre (745-mile) stretch of the Algerian coastline. One of the ports was Icosium, the ancient city on which Algiers now stands.
Archaeologists believe Icosium would have been founded in the 3rd century BC although they admit their knowledge is limited. Among the few clues so far was a pot of money discovered during the building of a road near the Casbah. It contained coins with the Punic inscription for Icosium and the effigy of a man who could have been Melqart, a Phoenician god.
Aware of the value of the heritage that is only now coming to light, the Algerian authorities hope to incorporate it into the site of the future metro station. They have asked INRAP to help come up with ways of preserving this unique archaeological heritage - proof of more than 2,000 years of Algerian history.