Part of the fortifications along Marsamxett Road, Valletta was defaced when someone spilled spent engine oil down the bastion on Thursday night.

Apart from condemning the vandalism, The Malta Environment and Planning Authority, (Mepa) has asked the police administrative law enforcement unit to investigate the criminal act.

The oil was probably dumped in the water run-off gutter on top of the bastion which forms part of the fortification known as the German Curtain.

The oil probably ran along a spout or a fissure and cascaded down the face of the bastion to the road below.

Mepa said that, according to restoration experts, it will not be easy to remove the smudge and the stain will probably be permanent.

The fortifications are scheduled as Grade 1 property (Harbour Fortifications).

Heritage Malta chairman Mario Tabone strongly condemned the vandalism calling it "a shame and a lack of sensitivity" for the national heritage, especially the fortifications. Such an act disturbs and disgusts those who hold the country's heritage at heart, he said.

The fortifications are extremely important because they feature in a substantial part of the island's military history. Heritage Malta condemns all forms of vandalism that undermined the country's identity and heritage, Dr Tabone said.

The attack on the fortifications comes at a time when the government has acquired millions of euros from the EU to restore the 27 kilometres of fortifications around the Maltese islands.