Two ancient sites in Athens. Hadrian’s Library has 1 ticket or tour to book; Roman Agora of Athens has no online ticket listed. The table and the two notes below put them side by side; the full pages have what to see, the ticket and the timing for each.
Hadrian's Library is the great colonnaded building the emperor Hadrian gave Athens in AD 132, on the north side of the Acropolis beside Monastiraki Square. Behind a facade of tall marble columns lay a courtyard with a long pool and halls where papyrus rolls were kept. Later the site held three churches in turn, whose remains are also on view.
The Roman Agora of Athens is the marketplace built with money from Julius Caesar and Augustus in the last decades BC, a short walk east of the older Greek Agora. Its star is the Tower of the Winds, an octagonal marble clock tower that survives almost complete. The site is small, central and quick to see.