The galleries found underneath Rua da Prata (Silver Street) in downtown Lisbon are estimated to have been built in the 1st century AD, during the peak of the Roman Empire. Over the centuries, the Roman structures on the surface crumbled or were replaced by new buildings. However, newer buildings were continuously constructed on the pre-existing Roman foundations.
This cryptoporticus was discovered after the 1755 Great Earthquake.
Public access is only possible 3 days a year after pumping out all the water accumulated over the entire year and the installation of lights (video). Water pumps continue work until the monument is once again closed to the public due to the significant rate of water seepage.