Speechless. Seething. Ready to ram their cans to kingdom come. It's how I felt yesterday when I read about the desecration of ancient cave paintings in Western Sahara, vandalised with spray paint by UN peacekeeping officers. The wretched men had tagged their names – sometimes in letters a metre high – over walls that also bore beautiful prehistoric daubings of giraffes, buffalo and elephants.
As with so much graffiti, the crime was also the confession: all they had the imagination to write were their names. "Evgeny" also scrawled "AUI", the code for the UN base in Aguanit; "Ibrahim", most helpfully, added his personal military number.
In my mind, they are being punished with Bosch-like ingenuity in the special corner of hell devoted to crimes against art. (Some say Jack Vettriano is also there, being tickled with a paintbrush.) In reality, the vandals' employers have made a conspicuously limp response. The UN's spokesperson for Western Sahara and Minurso is on the record as "appalled", and has said, "You would think some of them should know better. These are officers, not squaddies."
But all he has said as regards their penalty is: "We will report it to the troop-contributing countries. We can move them [the offenders]." Relocation hardly seems to fit the crime. When you consider the flow of tourism that this rock art, preserved and curated, might have brought to the region in the future, the economic loss to Western Sahara/Morocco must be considerable. And that's simply looking at it coolly from a profit/loss perspective. The cultural damage – particularly to the local Sahwari people, for whom the site has a mystical significance – isn't quantifiable.
What on earth were they thinking, these men? It would be nice to write it off as aberrant behaviour, but the urge to leave your mark where you shouldn't is one of our innate weaknesses. We've all had it, whether we acted on it or not. There were little personal scrawlings everywhere at school and university – particularly in the loos, of course.
Graffiti – the rudimentary, scrawled kind – is a human variant on cocking a leg. Our dog is especially keen to leave his calling card on a wall that the rest of the neighbourhood mutts have found choice; similarly, graffiti breeds graffiti, making a guttural sort of conversation. The ancient location in that cave in Western Sahara, site of many scrawlings from prehistory and Roman times onwards, clearly brought out a deep, dark troglodytic impulse in the vandals. The reason their super-egos did not kick in before the paint spray was discharged is a mystery, but it could have something to do with the history of graffiti to date. As you will see from this brief selection of key moments, our attitude to it is far from consistent.
Pompeii, c.AD100. Graffiti problem across town. Not illegal, but largely profane; described as "loathsome scribbles". Vesuvius erupts, and said graffiti becomes cherished history. Time + trash = treasure.
Early Christian era. Wall-scratching gets political. The anti-Christian/anti-Semitic Alexamenos graffito, found near the Palantine Hill in Rome, depicts Christ as a donkey. "Alexamenos loves God" is scrawled sarcastically underneath. Neither big nor clever.
Renaissance. Nero's buried home in Rome, the Domus Aurea, is explored by artists such as Filippino Lippi, Raphael and Michelangelo, who carve their names on the walls. "I woz here" has never been so elegantly executed.
Romantic period. We're beginning to see graffiti as the preserve of the frustrated and disenfranchised, the penniless, low-status outsider. Then we see "Byron" carved on the temple of Poseidon in Greece.
Twentieth century. A Frenchwoman enters the Louvre, approaches Ingres' painting The Sistine Chapel, and cuts out the eyes of the pope with nail scissors. She also slashes a cardinal. Her aim is to be arrested and imprisoned. Police officers oblige.
The Chapman Brothers buy a complete set of Goya's Disasters of War prints, and change all the visible victims' heads to those of clowns and puppies. For this they are commended in the art press.
Recent. Huge clean-up operations on urban graffiti; arrests, fines and Asbos common. A Banksy sells for £288,000 at Bonhams.
The messages are as mixed as a contemporary hospital ward. Of course, the marks we make on our surroundings are always going to hover between transgression and ornament, between defacement and distinguished art. But when the lines are too blurred, it can have damaging effects on common perception of boundaries.
Vandalism can come from egotism, fear, frustration or insanity. It looks as if it will always be with us, and part of its inherent quality is that it is essentially illogical, a cry in the dark. But while we might never be able to excuse it, it's surely worth trying to explain it.