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There are four of them each named after a Roman God. The Mercury Stone was already placed when Lara entered the adventure in Rome. However its centre piece also called the Mercury stone was missing which she claimed off Pierre Du Pont and Larson.
The Saturn Symbol can be found in the temple in the Streets of Rome. The Mars symbol is guarded by the Centurian Head in Trajan's Markets. The Venus symbol lies near the waterfall, behind a gate in the same level, although the gate cannot be opened until the Bronze Statue has been defeated.