The Museu Arqueológico on Rua das Portas de Loulé is the main museum of the city and it earns its place on the itinerary primarily for one unusual feature: a large Arab water cistern, discovered during construction of the building and left in situ beneath a glass floor. The cistern dates from the Almohad period (twelfth to thirteenth century) and is about 10 metres deep, with carefully fitted stone walls still largely intact. You look down into it from above, and the scale and quality of the Moorish engineering is genuinely striking.
The permanent collection traces the archaeology of the Silves region from the Chalcolithic through the Roman and Islamic periods, with a particular emphasis on the city's Muslim past. Exhibits include ceramics, tools, architectural fragments, and a range of small finds from the various excavations in and around the historic centre. The Roman-era material tends to get less attention than it deserves; there is a good selection of Sigillata ware and the usual range of amphorae.
Open Monday to Saturday. Allow forty-five minutes to an hour.