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," said Zetta Antonopoulou, an architect who has conducted extensive research on Athens statues, many of which are routinely marked with spray paint.

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

The "art form" has come a long way since 1810.

It was then that a young tourist in Greece carved his name into the ancient temple of Poseidon at Cape Sounio south of Athens.

Little did he know that the scrawl would become a cherished part of modern Greek heritage.

The traveller was 22-year-old George Gordon, Lord Byron, the maverick English poet who died fighting alongside the Greeks in their war of liberation against the Ottoman Empire and who is considered a national hero here.

Two centuries later, Greek archaeologists are proud of young Byron's handiwork -- but contemporary graffiti artists are not as welcome.

"The mark left by Byron is a historical document ... youths today write slogans, it's not the same thing," says Miranda Karatza, an archaeologist who heads the Greek culture ministry's sites and monuments office.

While other forms of graffiti related to sports or politics have been around for a long time in Greece, many Athenians remain unaccustomed to the latest phenomenon of street art and wall tagging by young "crews" marking territory.

"Graffiti is vandalism, it's an element of conflict, and sometimes things that are nice are also ruined," said Fotis, a 28-year-old street artist.

Fotis, who paints lizards and dragons, said he turned to graffiti as a way out of hooliganism and substance abuse but also in reaction to growing up in "a city full of ugliness and hate".

While full-fledged street art in Athens mostly keeps to the suburbs and alleys around the centre, quick-fix tagging on the city's main squares and public monuments is the clearest indication of the trend.

"A certain level of tagging is unavoidable in any city but in Athens it has been allowed to run riot," a reader recently commented in local English language weekly Athens Plus.

"More depressing still is the corresponding lack of any concern about it."

One striking example is Syntagma Square, one of Athens' busiest gathering points which recently became a popular hangout for teen skateboarders.

"We have to send crews to clean the walls and steps around once a month," says Alexandros Pouloudis, a supervisor at Athens' city maintenance office, noting that a comprehensive cleanup can cost up to 2,000 euros (2,950 dollars).

In the case of statues and monuments that must be carefully restored, the cost can exceed 20,000 euros, adds conservation expert Bessy Argyropoulou.

"The longer graffiti remains on stone or marble the more it is absorbed," she says. "It's not a quick and dirty operation like washing a car."

Closely associated with hip hop and rap music, street art arrived in Greece in the early 1990s and experienced a boom ahead of the Athens 2004 Olympics, says Antonis Katsouris, an urban culture writer for Highlights magazine.

"Graffiti is an identity statement in a hostile urban environment," he said. "And hip hop and rap are very popular in the poorer Athens districts."

Within a decade, a group of young painters inspired by Greek folk art and iconography caught the eye of art galleries, entered the mainstream and started taking commissions from hotels and restaurants.

"That generation has since abandoned the street (and) artistic graffiti is no longer as prevalent," he said.

"But tagging is going strong, and there is certainly no shortage of walls in Athens."