The Military Museum sits in front of the Santa Apolónia Station, not far from Terreiro do Paço and Castelo de São Jorge. It's on the site of a shipyard built during the reign of Manuel I (1495-1521). During the reign of João III, a new foundry for artillery was erected; it was also used for making gunpowder and storing arms to equip the Portuguese fleet. A fire damaged the buildings in 1726, and the 1755 earthquake destroyed them completely. Rebuilt on the orders of José I, the complex was designated as the Royal Army Arsenal. The museum, originally called the Artillery Museum, was created in 1851. Today the facility exhibits not only arms, but also paintings, sculpture, tiles, and examples of architecture.

The museum boasts one of the world's best collections of historical artillery. Bronze cannons of various periods include one from Diu, weighing 20 tons and bearing Arabic inscriptions. Some iron pieces date from the 14th century. Light weapons, such as guns, pistols, and swords, are displayed in cases.