Roman emperors Valentinian I, Valens, and Gratian issue a new law exempting women who have dedicated themselves to Christianity from the "tax of the people." This law benefits Christians over adherents of other religions who have to continue paying all the usual taxes.
The new Roman law states:
"...any women who have dedicated themselves to the perpetual service of the sacred law shall be held exempt from such public service" [CTh 13.10.6]
It is thought that this "tax of the people" is likely a poll tax.