The Constitutio Antoniniana (Latin: "Constitution of Antoninus") was an edict declared in 212 AD by the Roman Emperor Caracalla (whose real name was Marcus Aurelius Antoninus). The law declared that all free-born men of the Roman Empire were to be given full Roman citizenship, and all free-born women of the Empire were given the same rights as Roman women were.
Before 212, for the most part only Italians held full Roman citizenship. Colonies of Italians established in other provinces, Italians (or their descendents) living in colonies, the inhabitants of various cities throughout the Empire, and small amounts of local nobles (such as client-kings) all held full citizenship also, while at most, the majority of provincials merely held limited Roman citizenship rights (if that at all).
The reasons Caracalla passed this law were mainly to increase the number of people available to tax and to serve in the legions (only full citizens could serve in the Roman army). However, it had the unintended aftereffect of allowing provincials the hope of becoming emperor, and of starting uprisings with that hope in mind (the first to do so being Maximinus Thrax only 23 years after this edict); this would play a major factor in the Crisis of the Third Century and the eventual fall of the Roman Empire.
