You will be given a definition of a task first, then some input of the task.
You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: U.S. LANDMARKS 
Clue: It contains over 5,000 tons of steel, rises 630 feet in the air & is in the shape of an inverted catenary curve
Output:
the st. louis gateway arch