The authorities call it a Greek tragedy, but the graffiti artists who have increasingly left their mark on this ancient city and its monuments say they are simply responding to a different sort of muse.

Churches and archaeological sites in Greece used to enjoy a certain immunity from graffiti and the stylised signatures known as tagging, but are now increasingly part of the action as the phenomenon takes off in Athens.

"There is an inability to distinguish what is a monument, and what is not in Athens," said Zetta Antonopoulou, an architect who has conducted extensive research on the capital's statues, many of which are routinely marked with spray paint.

"It's getting out of control and it's not easy to explain why."