The Obelisk Garden provides population and coins. When the Obelisk Garden is motivated, its production is doubled and it produces 1 Forge Point. The production is also affected by the town's happiness and by boosts of certain Great Buildings. The Obelisk Garden can be plundered if it isn't motivated.
The building also has a secondary effect, i.e. the player will be able to spot Cleopatra herself being carried around in her lectica!