Under which Roman emperor was Roman citizenship extended to all free male inhabitants of the Roman Empire?
Caracalla was the popular nickname of Marcus Aurelius Severus Antoninus Augustus, Roman emperor (AD 198–217). The eldest son of Septimius Severus, Caracalla reigned jointly with his father from 198 until Severus' death in 211. For a short time Caracalla then ruled jointly with his younger brother Geta until Caracalla had Geta murdered later in 211. Caracalla is remembered as one of the most notorious and unpleasant of emperors (according to the literate elite) because of the massacres and persecutions he authorized and instigated throughout the Empire.
Caracalla's reign was also notable for the Constitutio Antoniniana (also called the Edict of Caracalla or the Antonine Constitution), granting Roman citizenship to all freemen throughout the Roman Empire, which according to the hostile historian Cassius Dio, was done for the purposes of raising tax revenue. This edict was issued in 212 AD. Caracalla also commissioned a large public bath-house (thermae) project in Rome, and the remains of the Baths of Caracalla are still one of the major tourist attractions of the Italian capital.