We
only known about this from Eusebius Life
of Constantine.
AD 331 Emperor requested 50 new
Bibles (Books of Scriptures) from Eusebius for churches in
Constantinople
Eusebius had the copies made at his home
church of Caesarea
There was no decision by Constantine as
to which books they should contain. Both he and Eusebius
understood and assumed which texts were part of Scripture.