On what day was Jesus born according to the gospels and how was the date of December 25 agreed?

To all this we must add one more circumstance: the possibility that these chapters, Matthew 1 and 2, and Luke 1 and 2, were added to the respective gospels since they were already circulating, explains to BBC News Mundo Antonio Piñero, professor emeritus of Greek Philology at the Complutense University of Madrid, in Spain, whose study focused on the language and literature of early Christianity.