Aqueduct of Hadrian in Athens, Roman aqueduct in Attica Region, Greece

The Aqueduct of Hadrian is a roughly 19.7 km Roman water conduit that ran mostly in a vaulted tunnel from the area of today's Tatoi, on Mount Parnitha, to a reservoir on the slope of Lykavittos. Tunnel sections were about 0.7–0.8 m wide and 1.1–1.6 m high. The best-preserved bridge section stands in Nea Ionia, on both sides of Kapodistriou Avenue near Plateia Adrianeiou.

Work on the aqueduct began in 134 AD under Hadrian and was finished in 140 AD under his successor Antoninus Pius, whose inscription records that he completed and dedicated his father's project in the New Athens. The 25 km line ran from the Tatoi area to a 500 m³ stone reservoir at the foot of Lykavittos. It kept working through the Ottoman period, until Hatzi-Ali Haseki destroyed it; mayors Kyriakos and Soutsos later had it cleaned and reopened.

The Latin dedication on the reservoir's propylon names Antoninus Pius as the emperor who completed and dedicated the aqueduct begun by his deified father Hadrian, in the "New Athens". The left part of that inscription is kept in the National Garden. Water from the system fed the Roman baths at Zappeion and the Nymphaion of the Agora.

The passage is narrow and low, requiring visitors to bend down if exploring inside, so preparation for tight spaces is necessary. Visit during dry periods when possible, as some sections may have standing water and slippery surfaces.

A section of the aqueduct was rediscovered in 1870 and used to irrigate the Royal Garden, today's National Garden. The best-preserved bridge stretch stands in Néa Ionía on both sides of Kapodistríou avenue near Plateía Adrianeíou, though some scholars attribute it to a later 4th-century aqueduct.