Complutum was the Roman city that preceded medieval Alcalá, and its forum — a significant archaeological site — lies about a kilometre outside the current city centre, partially excavated and accessible to visitors. The site reveals the basilica, marketplace, public baths, and cryptoporticus (a vaulted underground passage) of a prosperous Roman settlement that thrived from the first century AD until its eventual abandonment.
The Regional Archaeological Museum of the Community of Madrid, in the city centre, holds the most spectacular finds from Complutum, including a remarkable collection of Roman mosaics and domestic mural paintings that give vivid colour to what life looked like here two thousand years ago. Visiting both the museum and the forum together provides the most complete picture. The forum site itself is open-air and free; the museum requires a ticket.