Having just passed under the aqueduct by random chance on a quick subway ride, I must say the Agua Livres Aqueduct had quite an impact. Although it's true that many impressive aqueducts were made around the same time period as it, it is uniquely majestic as being situated in and serving the heart of a world-class city like Lisbon. If not on its own merits, I'd love to see the aqueduct with World Heritage status even as part of a more comprehensive Lisbon site, and I do think that design-wise, its vast arches are really quite a unique and graceful sight to behold.