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: THE 7 WONDERS OF THE WORLD
Clue: Philo of Byzantium called it a ploughed field "above the heads of those who walk between the columns below"
the hanging gardens of babylon