Emperor Constantine the Great issues a new law that if a slave is freed in front of a bishop they will automatically become Roman citizens.
According to Constantine's law:
"If anyone with pious intent grants freedom to his slaves in the bosom of the Church, it shall have the same legal force as that with which Roman citizenship formerly was bestowed. But the right to free slaves in church shall be allowed under the eyes of the bishops.
Priests who free their own household slaves may do so in sight of the Church and the religious congregation or in a last will or ordered it to be given by any words. Either way, the slaves will be freed immediately on the publication of the will, without the necessity of any witness or intermediary of the law. [CTh 4.7.1]