After some debate about the exact location of the tower, a contract was signed on 8 January 1887. This was signed by Eiffel acting in his own capacity rather than as the representative of his company, and granted him 1.5 million francs toward the construction costs: less than a quarter of the estimated 6.5 million francs. Eiffel was to receive all income from the commercial exploitation of the tower during the exhibition and for the next 20 years. He later established a separate company to manage the tower, putting up half the necessary capital himself.
Work on the foundations started on 28 January 1887. Those for the east and south legs were straightforward, with each leg resting on four 2 m (6.6 ft) concrete slabs, one for each of the principal girders of each leg. The west and north legs, being closer to the river Seine, were more complicated: each slab needed two piles installed by using compressed-air caissons 15 m (49 ft) long and 6 m (20 ft) in diameter driven to a depth of 22 m (72 ft) to support the concrete slabs, which were 6 m (20 ft) thick. Each of these slabs supported a block of limestone with an inclined top to bear a supporting shoe for the ironwork.