Emilie Nouguier and Maurice Koechlin were the two chief engineers in Eiffel's company. The conceived of the idea for a very tall tower in June of 1884. It was to be like a large pylon with four columns of lattice work girders, separated at the base and coming together at the top and joined to each other by more metal girders. Eiffel's company already had mastered the principle of building bridge supports so they wanted to take that a step further. The tower project was a bold extension of this principle up to a height of 300 meters, 1000 feet. On September 18, 1884, Eiffel registered a patent for allowing of the construction of metal supports and pylons exceeding the height of 300 meters.

The Koechlin's plan.
(Click to enlarge)

To make the tower more visually pleasing, Nouguier and Koechilin hired the architect Stephen Sauvestre to work on the appearance of the tower. Sauvestre proposed stonework pedestals under the legs, monumental arches to link the columns and the first level, large glass-walled halls on each level, a bulb-shaped design for the top and other features to decorate the structure. In the end, the project was simplified although some of the characteristics planned were kept, such as the large arches.

The curvature of the tower's legs are mathematically determined to offer the most efficient wind resistance possible. Eiffel explains, "All the cutting force of the wind passes into the interior of the leading edge uprights. Lines drawn tangential to each upright with the point of each tangent at the same height, will always intersect at a second point, which is exactly the point through which passes the flow resultant from the action of the wind on that part of the tower support situated above the two points in question. Before coming together at the high pinnacle, the uprights appear to burst out of the ground, and in a way to be shaped by the action of the wind."