Strabo's Geographica or Geography (Greek: Γεωγραφικά) is the most important work on its subject to survive from the ancient world, giving a comprehensive account of those parts of Europe, Asia and Africa known to the Romans.
It's author, Strabo, came from a well-to-do Greek family in the city of Amasia, Pontus, and was born in around 64 BC. His early education at Rome was the prelude to extensive travels in the Near East. He adopted a Stoic philosophy which influenced a cosmopolitan admiration for the Romans. His lost Historical Sketches covered the periods before and after the work of Polybius, up to the time of Julius Caesar. The Geography may have been completed around around 7BC and revised in 18 AD.
Free online texts
Internet Archive: L 049 - Strabo - Geography I. Greek and English text. Loeb edition, multiple formats.
LacusCurtius: Strabo's Geography. English translation by H.L. Jones. HTML format.
Loebulus: L049 - Strabo -- Geography I: Books 1-2 | L211 - Strabo -- Geography V: Books 10-12 | L223 - Strabo -- Geography VI: Books 13-14 | L241 - Strabo -- Geography VII: Books 15-16 | L267 - Strabo -- Geography VIII: Book 17 and General Index. Greek and English text. Loeb edition, PDF format.
Ancient World Mapping Center: Strabo Map.
BBC In Our Time: Strabo's Geographica. Melvyn Bragg in radio conversation with Paul Cartledge, Maria Pretzler, and Benet Salway.
Cartographic-images.net: Strabo's World Map.
Strabo the Geographer - Site by Sarah Pothecary.
The Great Conversation: Further reading at Tom's Learning Notes
Herodotus: The Histories.
Polybius: The Histories.
Pliny the Elder: Natural History - a similarly encyclopaedic writer who seems to have been oddly unaware of Strabo's work.
Ancient Greek resources: Learn to read Greek classics in the original.