The Eiffel Tower would be built on the Champ de Mars. The Champ de Mars is a field on the Left Bank of the Seine River in central Paris, where part of the fair was to be held. The tower would serve as a main entrance to the fair. Eiffel took Koechlin’s design and began to plan the construction. Eiffel measured, tested, and planned for every detail. He wanted a drawing of each piece of the tower. Fifty engineers and designers produced fifty-
The drawings used more than 14,000 square feet (1,300 sq. m) of paper. Eiffel also began testing the ground under the Champs de Mars. Close to the river, the ground had a top layer of sand and gravel 20 feet (6 m) deep. Eiffel could not build on that, so he backed up from the river until he found solid ground. Workers broke ground (began digging) on January 26, 1887.