An obelisk is a monolithic stone monument whose four sides, which generally carry inscriptions, gently taper into a pyramidion at the top. The ancient Egyptians usually erected them in pairs and associated them with the rays of the Sun, which increase in width as they reach the Earth. The earliest known examples, excavated at Abu Sir, Egypt, date from the Old Kingdom during the reign of Neuserre (2449-2417 BC). The unfinished obelisk in the quarry at Aswan shows how these monuments, some more than 32 m (105 ft) long, were cut as single pieces of red granite. Their transport on barges down the Nile is depicted on relief sculptures. So popular were these monuments among the Roman emperors that 13 of them were taken to Rome. Today, in addition to CLEOPATRA's NEEDLES in London and New York, historic Egyptian examples stand in Paris, Florence, and Rome. Cleopatra's Needles, named for the famous Egyptian queen, are two ancient OBELISKS presented by the khedive of Egypt to Great Britain (187 and the United States (1880). The British monument, 20.9 m (68.5 ft) high, is located on the Thames Embankment in London. The American one, 21.2 m (69.5 ft) high, stands in New York City's Central Park. They were originally erected c.1500 BC in the city of HELIOPOLIS by THUTMOSE III. In 14 BC, Augustus ordered their removal to Alexandria to grace the grounds of the Caesareum. The British installed their obelisk at its present location in 1878; the Americans did so in 1881. Carved from rose-colored Syrene granite and inscribed with HIEROGLYPHICS, each weighs approximately 200 tons. In recent years, the surfaces of the obelisks have eroded because of moist air and urban pollution.