The church was left abandoned for years.

Two decades following its restoration, cracks have reappeared on the walls of the old Birkirkara church, which has a long history of structural problems and at one point was left for a whole century without a roof.

According to monitoring by University of Malta researchers, there are strong indications the cracks are developing, and pieces of mortar have even fallen from the vault of the main nave.

The structure is still safe, but hundreds of thousands of euros are needed to avoid further damage to the church, which dates to the 17th century.

According to research by historian Sandro Sciberras, the Church of the Assumption in Birkirkara, known as il-Knisja l-Qadima, was the first collegiate established in the Maltese Islands after the one in Mdina.

It is estimated that the church took around 50 years to build and was in use up to the early 18th century, when the people of Birkirkara decided to build a new and bigger church closer to the old village centre.

The cracks seem to be developing, and mortar has fallen from the main nave

Then in 1787, Bishop Labini ordered the sealing of the church, as it had developed visible structural problems. The first parts of the barrel vault collapsed in 1830, and an earthquake soon after brought down part of the roof. The dome finally collapsed between 1850 and 1860.

It was not until the 1960s and 70s that restoration kicked off, continuing in the 1990s – when the church started to receive parishioners once again.

But trouble is brewing again.

The church is often praised for its architectural beauty and historical importance. One side is covered with shrapnel dents, probably dating back to when the French occupied Malta.

The church was originally planned by Vittorio Cassar, son of Girolamo Cassar, and continued by Tommaso Dingli, who planned a few of Malta’s most important 17th-century churches, such as those in Żebbuġ, Naxxar, St George’s in Qormi, Balzan and Attard.

In recent years the church has drawn the attention of researchers including university lecturer Adrian Mifsud, who is studying its foundations and carrying out tests on the underlying rock as part of his doctorate.

The geotechnical engineer told this newspaper that the church’s walls were gradually leaning outwards like a blossoming flower. Measurements show that the church is some 20cm wider at the top than at the bottom.

Meanwhile, the dome is weighing down the pillars holding it, pushing them at least eight centimetres down.

A monitoring system, including for cracks, has been installed indoors and outdoors on the church’s walls and ceilings to help the researchers understand this movement and also to raise the alarm should the place become unsafe.

The cracks were first documented in 2006 by Heritage Malta in a report that suggested that ground conditions beneath the church could have caused these structural movements.

University researchers later drilled boreholes within and below the foundations, with the recovered cores being inspected in a laboratory.

Built during the transitional period between the Renaissance and the introduction of the Baroque, the church has elements of both styles.

It was discovered that beneath a relatively hard but very thin layer of rock below the church foundations, there is a thick layer of marl (turbazz) – a very weak rock or clay stone.

A trial pit was also excavated next to the facade of the church, with block samples of the weaker rock material taken for subsequent analysis.

Mr Mifsud noted that estimates for the required work are still being worked out, because there has not yet been any research on marl in Malta. Mr Mifsud, who is currently carrying out studies on the material, has also found support from his colleagues from the Faculty  of Engineering in setting up the monitoring system and building up their laboratory equipment.

The first parts of the barrel vault at the Church of the Assumption in Birkirkara collapsed in 1830, and the dome collapsed between 1850 and 1860.

The church’s walls are gradually leaning outwards like a blossoming flower. Measurements show that it is some 20cm wider at the top than at the bottom.

Crack monitors help the researchers understand the movements starting from the foundations.

The church once had a dome, as seen in this illustration.