Twice a year, a hatch in a busy Lisbon street opens to reveal steps leading to one of the Portuguese capital's most ancient sites: a 2,000-year-old Roman structure that still holds the buildings above it together.
Dating back to the first century AD, the "cryptoportico" subterranean maze of tunnels and passageways was built by the Romans, who occupied the city then known as Olissipo beginning around 200 BC. The city remained under Roman control for several centuries.
