Thiseio

thumb|220px|right|The "Temple of Theseus" ([[Temple of Hephaestus), after which the area was named]] thumb|220px|left|upright|Statue of Theseus outside the [[Thiseio metro station]] thumb|The Entry of King Otto of Greece into Athens by [[Peter von Hess, 1839]] thumb|left|Line 1 (Athens Metro)|A metro line between the [[Stoa of Attalos and a basilica's ruins]] thumb|right|The Byzantine Church of the Holy Apostles, Athens|Church of the Holy Apostles next to the [[Stoa of Attalos]] thumb|right|The Roman-era Philopappos Monument thumb|left|The Odeon of Herodes Atticus, open-air ancient theatre 230px|thumb|left|The National Observatory of Athens|National Observatory atop the Hill of Nymphon

Thiseio or Thissio (, ) is a traditional neighbourhood in the old city of Athens, Greece, northwest of the Acropolis, and surrounded by the archaeological sites of the Agora, Keramikos and Pnyx. The name refers to the Temple of Hephaestus, which was mistakenly known as Thiseion, in reference to Theseus, the mythical king of Athens.