It's become fashionable to commemorate things. Just last week, a friend who decided not to leave work threw a party to commemorate that fact. And what could be a better way of marking this unending stream of important events than a mobile monument? Such an object, created by Mexican artist Damian Ortega, stands just outside Central Park in the Dorothy C. Freedman Plaza. Obelisco Transportable (right) is a 6.5-metre-high obelisk that looks like a smaller, shiny black version of one of Cleopatra's Needles. It appears to be a permanent installation. But it's on a set of wheels so it can be pushed from location to location. This transportable obelisk would be a handy purchase for institutions wanting to commemorate events without having the expense of commissioning a new monument each time. But that's not Ortega's idea. It's a piece of concept art made to express the notion that, although monuments are created for a specific location, they often end up somewhere else. Usually, Ortega says, they have been removed from their original locations by victorious armies and deposited in the victor's lands as a symbol of victory. Ortega calls this the 'Napoleonic gesture'. Cleopatra's Needles, which provided the model for Obelisco Transportable, are a case in point. They've all been about a bit. One stands on the banks of the Thames in London, one in New York's Central Park and one is in Paris. The Needles were originally created in the Egyptian city of Heliopolis in 1450BC. The Romans moved them to Alexandria in 12BC and they ended up in a temple devoted to Roman general Marcus Antonius. Mehmet Ali, the Viceroy of Egypt, sent them as gifts to the three 'great powers' during the 19th century. Ortega was a political cartoonist in Mexico. He tries to create work which 'taps into the poetic and symbolic resonance of everyday forms'. He likes to investigate 'the way objects serve as markers of cultural and political history'. Things with wheels seem to fascinate him. His last big work was the Beetle Trilogy, which explored the iconic status of the Volkswagen Beetle car. It's possible Ortega's idea of mobile monuments will catch on. If wheels were added to Nelson's Column in London, it could be pushed down the Mall during the Trooping of the Colour ceremony, or moved to attend royal garden parties. If wheels were added to the Arc De Triomphe, the French could move it to create a traffic jam. Or the idea could be taken up by Ikea, which could make Obeliscos Transportables to commemorate office parties.