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This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.

Passage: Gallaeci lived in castros. These were usually annular forts, with one or more concentric earthen or stony walls, with a trench in front of each one. They were frequently located at hills, or in seashore cliffs and peninsulas. Some well known castros can be found, in the seashore, at Fazouro, Santa Tegra, Barona and O Neixon, and inland at San Cibrao de Las, Borneiro, Castromao, and Viladonga. Some other distinctive features, such as temples, baths, reservoirs, warrior statues and decorative carvings have been found associated to this culture, together with rich gold and metalworking traditions. Question: Where were these forts commonly built?
Output:
hills