In downtown Athens and in the area behind the ruined temple of Zeus lies the unknown to many Basilica of Leonidis, the oldest Christian monument of the capital. It was erected in the fifth century in honour of Leonidis, bishop of Athens, who suffered martyrdom in 250 AD during Decius persecution.
The building was a representative example of the transitional type — from the simple, timber roofed to the domed basilica. The late G. Soteriou made the thorough excavation and study of the church during the years 1916-1917.
The basilica was probably founded in the years 423-450 by the Byzantine Empress Athenais-Eudocia, wife of the Emperor Theodosiue II .Adjacent to the basilica was a crypte-martyrium, where Leonidis’ relics were kept, and another edifice, a baptisterium, in all probability. The basilica itself was very carefully built and richly decorated with marble walls, mosaics and sculpture. This Early Christian monument of Ilissos properly fills the gap in the continuous artistic and cultural evolution of the city of Athens.