According to Herodotus, Darius I established 20 satrapies.
A satrapy was a province of the Achaemenid Persian Empire, governed by a satrap, an official appointed by the king. Darius I reorganized the empire’s administration after taking power in 522 BC, creating a more systematic structure for taxation, tribute and provincial oversight. Herodotus lists the satrapies and the tribute assigned to them in Book 3 of his Histories.
The figure 20 needs its historical qualifier. It refers to Herodotus’s account, not necessarily an unchanging total for every year of Darius’s reign. Persian administrative divisions could change, and ancient sources do not always use identical classifications. Herodotus’s list also treats Persis, the Persian homeland, differently from the tribute-paying provinces.
Satraps had substantial authority, but they were not fully independent rulers. The Great King monitored them through royal inspectors, military arrangements and competing officials. This balance between local administration and central supervision helped Persia govern a vast, culturally diverse empire.