Icosium (Greek: Ἰκόσιον): Phoenician colony, Roman city, modern Algiers.
- Founded by the Phoenicians; the site is more or less identical to the kasbah of modern Algiers
- The name may be derived from Numidic wyksm, "island of seagulls" (the modern Arabic name, الجزائر, also means island)
- Becomes part of the Roman world after the Third Punic War (146 BCE); taken into possession by the kings of Numidia and Mauretania; finally annexed when the emperor Caligula has king Ptolemy of Mauretania assassinated (40 CE)
- Some Roman remains, but poorly understood
- Main excavation: Bab el-Oued, the cemetery directly outside the northern city gate