The Romans used shafts like the four-metre deep examples at Augusta Raurica – some 20 kilometres from Basel – as cool stores during summer.

The shafts were filled with snow and ice during winter and then covered with straw to keep the space cool well into the summer months. This then allowed for everything from cheese to wine – and even oysters – to be preserved during warm weather.

Now a team lead by Peter-Andrew Schwarz from the University of Basel is attempting, for the third time, to demonstrate that the Augusta Raurica shafts were indeed used as fridges, Swiss news agency SDA/ATS reports.

A first attempt to recreate the ancient cool box failed after archaeologists at the dig filed the shaft with snow all in one go. But that experiment showed temperatures in the shaft were above freezing point even in winter.

The second try was more successful: the shaft was gradually filled with snow and ice blocks were placed inside as well. Using these methods, snow remained until June.

Now, however, researchers plan to use methods developed by the so-called ‘nevaters’ or ice-makers on the Spanish island of Majorca. This will see Schwarz and his team placing 20–30-centimetre-thick layers of snow into the shaft. These individual layers will then be compacted down with a straw cover placed on top of each one.

“With this method, people in Majorca could keep food cool in summer before the arrival of electric fridges,” Schwarz told regional daily Basler Zeitung in 2017.

Work at the site of the 'fridge' will continue until Friday with the dig open to the public.

The experiment won’t prove that the mysterious shaft was actually a Roman fridge but will show that this is possible, Schwarz told the SDA/ATS news agency.

A final evaluation will be made in August.