A mysterious cross has been discovered underneath the City Market in Nairobi, triggering interest by archaeologists and architectural historians on what could be beneath the crucifix-like concrete.

The discovery, made by Nairobi Metropolitan workers who were digging the courtyard normally used by fishmongers to put a new floor, saw the work stop as archaeologists from the National Museums of Kenya were summoned to inspect the site.

The museums team dug around the cross slab which has some pipe points on it as workers wondered whether they had stumbled on a cemetery.

“What we found is that it is made of solid granite and beneath it there is another heavy concrete layer reinforced with heavy metal,” said Dr Emmanuel Ndiema, the archaeologist who assessed the site.

“We don’t know for sure whether it was an ablution block or its historical significance,” he added.

While it has no inscriptions on it, the cross was left intact by the museum’s team – hopin to in future, to x-ray underneath the slab.

“We shall use ground penetration radar or portable CT scan to check the site,” said Dr Ndiema.

City Market was built in 1930s as a European-only market to replace the Jeevanjee market, which had been brought down due to unsanitary conditions.

Interestingly, City Market’s interior architecture resembles London’s Royal Horticultural Lawrence Hall which was built in late 1920s and which won awards by its use of reinforced concrete.

It is not clear whether City Hall architects had any dealings with Sir Howard Robertson, the man who had made his name by popularising the tall parabolic arches, and what the uncovered cross could have meant.

While architecture students have always studied City Markets’s cavernous reinforced-concrete arches, the discovered reinforced concrete beneath will renew interest.