Why does the Eiffel Tower have four pillars?

The four pillars are used to support the tower and are aligned to the points of the compass.

The Eiffel towers has four pillars for stability, and to give it a symetrical aspect. The design was the object of a contest and only a four-legged design was considered at the time. Technically it would have been possible to build a resembling structure with only three pillars (like a three-legged stool instead).