Eiffel Tower In 1909, a permanent underground radio centre was built near the south pillar, which still exists today. On 20 November 1913, the Paris Observatory, using the Eiffel Tower as an aerial, exchanged wireless signals with the United States Naval Observatory, which used an aerial in Arlington, Virginia. The object of the transmissions was to measure the difference in longitude between Paris and Washington, D.C. Today, radio and digital television signals are transmitted from the Eiffel Tower. A television antenna was first installed on the tower in 1957, increasing its height by 18.7 m (61.4 ft). Work carried out in 2000
Philadelphia City Hall 1871 to 1901 at a cost of $24 million. City Hall's tower was completed by 1894, although the interior wasn't finished until 1901. Designed to be the world's tallest building, it was surpassed during construction by the Washington Monument and the Eiffel Tower. Upon completion of its tower in 1894, it became the world's tallest habitable building. It was also the first secular building to have this distinction, as all previous world's tallest buildings were religious structures, including European cathedrals and—for the previous 3,800 years—the Great Pyramid of Giza. With almost 700 rooms, City Hall is the largest municipal building