The historical Syntagma Square is central to the political and social life of Athens. The Square was named after the Constitution (= Syntagma in Greek) King Othon was forced to grant the people after a popular and military uprising, on September 3, 1843. During the excavations undertaken while constructing the metro system, many significant archaeological finds from the late Mycenaen period to the late Roman period (1100 BC - AD 300) were brought to light. Some of these finds are now exhibited in special showcases in the metro station.
More information: http://en.wikipedia.org/wiki/Syntagma_Square