Participants meet at 4 pm in front of the Obelisk monument on Avenida 9 de Julio.

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In 1878, the obelisk known as Cleopatra's Needle, originally cut from the quarries of Aswan in about 1475 BC, was erected in London.

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Tilting the obelisk in the Place de la Concorde, however, was not feasible, so a conversion chart nearby enables those who have forgotten their watches to make the appropriate corrections.

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Among the ideas under consideration are a bronze bust, a commemorative plaque and even an obelisk at the Imberhorne cutting, which represents the final obstacle to a complete Bluebell Railway.

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One of the largest is in the Place de la Concorde in Paris, where the 32m (108ft) Egyptian obelisk has, after a couple of false starts, been converted into a giant sundial with the help of a few judiciously placed markings on the pavement.

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The only real marker is a strangely unimposing obelisk, like a highway marker for some forlorn, forgotten incident.

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Helen Mahy, one of only a handful of women General Counsels in the UK, has agreed to become chairwoman of Obelisk's advisory board when she retires from her job as group company secretary at National Grid next year.

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Towering ahead is a colossal obelisk of red granite, which appears to rise directly out of the ocean.

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So a few years and a billion pounds or so later, the great architect delivers his monumental vision - a cloud-tickling skyscraper, a giant gleaming obelisk that emerges from London Bridge train station like a rocket about to take off.

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