Married priests were common in the early centuries, but were never the norm. Priestly celibacy in the West became the legal norm no later than the 4th century, in recognition of a practical norm that was believed at the time to date to the original Apostles. Moreover, sexual continence was expected within priestly marriages.
I would not rely on Pope Francis in this, as he has justly earned his reputation for careless, ill-considered speech.
According to Wikipedia.com (clerical celibacy):
“The tenth century is claimed to be the high point of clerical marriage in the Latin communion (Catholic Church). Most rural priests were married and many urban clergy and bishops had wives and children”
As for the reason why the need for compulsory clerical celibacy, the article further states:
“...a large number of clergy, not only priests but bishops, openly took wives and begot children to whom they transmitted their benefices...”
Regarding the Pope. I agree he’s a socialist and I wish they’d bring Pope Benedict XVI back out of retirement. However, Pope Francis made three observations about clerical celibacy which are entirely correct:
1) The policy is a discipline of the Church, not a dogma or doctrine.
2) The policy was implemented many centuries after the founding of the Church.
3) The policy is always subject to change.
All true.