An undated structure which has never been recorded in Gozo or Malta was unearthed during restoration works at the Citadel.

Approximately three metres in diameter, it consists of a round man-made feature cut in the bedrock (greensand layer) of Cathedral Square.

A series of large hardstone pebbles are set in an oval shape of around two metres in the middle of the feature.

They are resting on a layer of clay which was specifically put at the bottom. The larger pebbles are surrounded by smaller pebbles in the structure discovered last week.

“Its use and age are still unknown. Several hypotheses have been put forward, including a burial site, a well shaft or a hearth, but lack of cultural material is making it difficult to determine the age and purpose of this structure,” project leader John Cremona told the newspaper.

Its use and age are still unknown. Several hypotheses have been put forward, including a burial site, a well shaft or a hearth

No similar structures are known to exist either in Malta or in Gozo.

It was originally a complete circular feature but some years ago the feature was cut through right in the middle by a service trench, Mr Cremona said.

Restoration works at the Citadel have unearthed a mystery circle. Photo: Joseph Zammit

Meanwhile, not far off, a well and a shaft with an interconnecting tunnel were discovered during the same restoration works.

Mr Cremona explained that these were part of the water catchment system devised during the British period to collect water in the reservoirs.

The reservoirs are now being converted into a visitors’ centre, while the curious structure will be preserved in its original location.

Discussions on how this feature will remain visible to the public when the levelling and paving project of the piazza is completed are still going on, Mr Cremona added.

The restoration of the Citadel involves two EU co-funded projects. The restoration of its bastions was completed by December 2013. The other project, which started in March and planned to be completed by June, is themed Implementation of the Citadel Masterplan Recommendations.

Estimated to cost €14 million, the project also led to the discovery of the old main passageway. Dating to the 17th century, it leads to the main entrance of the Citadel and will be incorporated in the new gateway design.