Caracalla

Born Lucius Septimius Bassianus on 4 April 188, he became nominal co-emperor at ten when his father Septimius Severus named him joint ruler in 198, later doing the same for his younger brother Geta in 209. After Severus died in 211, the brothers shared power briefly before Caracalla had Geta killed by the Praetorian Guard and took sole control, leaving their mother Julia Domna to handle much of the administration he found boring. His reign brought domestic instability and Germanic incursions, but also the Antonine Constitution - which extended Roman citizenship to all free people in the empire - and the Baths of Caracalla, the second-largest bathing complex Rome ever built. He launched a campaign against Parthia in 216 but never finished it: a disgruntled soldier assassinated him on 8 April 217, three days before Macrinus claimed the throne.