The New Testament (Mk 1:29-31; Mt 8:14-15; Lk 4:38-39; 1 Tim 3:2, 12; Tit 1:6) makes it clear that at least one apostle was married, the Apostle Peter had a mother-in-law. It is also clear that bishops, priests, and deacons of the time were normally family men (husband of one wife). It is also clear from the testimony of the Church Fathers, from conciliar decrees, and much other written evidence that married clergy was a normal feature of the Church's life. Perhaps there were even married popes [St. Felix III 483-492 (2 children); St. Hormidas 514-523 (1 son); St. Silverus (Antonia) 536-537; Hadrian II 867-872 (1 daughter); Clement IV 1265-1268 (2 daughters); Felix V 1439-1449 (1 son)]. It does seem clear that marriage must precede the order and that once orders had been conferred, marriage and remarriage (for widowed) was prohibited. St. Boniface reported to the pope that in Germany almost no bishop or priest was celibate. But officially, from the 11th century on, celibacy has been in one way or another the obligatory discipline of the clergy at least in the West.
It arose after a clear narrowing of the legitimacy of clergy marriage and of having children progressed down the centuries. Lateran I (1123) codified the prohibition of cohabiting with wives. Lateran II (1139) reiterated the declaration of the Council of Pisa (1135), not only prohibiting marriages contracted subsequent to ordination but seemingly declaring them to be null and void. From the time of Alexander III (1159-1181) married men were not allowed ecclesiastical benefices. The rights of the wife were given the protection of life in a convent. In 1322 Pope John XXII insisted that no married man could be ordained. Some have found evidence that 50% of priests were married and accepted by the people in the 15th century. Despite the attacks of Luther and Zwingli upon celibacy, the Council of Trent (1562-3) resisted the pressure to modify the rules of celibacy were rejected. In Session XXIV on 11 November 1563, the Council upheld the prohibition of clerical marriage.
The Enlightenment saw fresh attacks upon clerical celibacy and in the wake of the First Vatican Council, the Old Catholics, separating themselves from Rome, abolished celibacy. Pope Benedict XV declared, December 16, 1920, that the Church considered celibacy to be of such importance that it could never abolish it. Following Vatican II, there were many voices in favor of relaxing the discipline and exceptions were made for married deacons of mature age and for married clergy seeking to enter into communion with Rome, to the point where there are more married clergy in the Western Rite of Rome now than ever before.
All of this is interesting especially in light of Pope Francis who remarked that it was really all about money, specifically the competing claims of family and the Roman Church on the inheritances of married clergy. "The Catholic Church began requiring celibacy in the 11th century because clergy with no children were more likely to leave their money to the church," so Pope Francis said, anyway. While it is true that celibacy was never dogma and always a discipline, a personal discipline as a sign of fealty to the Church, the Pope, and the bishop, it is not about to go away quietly. Further, the marriage of clergy will not end Rome's clergy problems of sexual attraction, pedophilia, and decreasing numbers. It is not a panacea. Celibacy is a promise made before the bishop at ordination. It could easily be undone and yet it is highly unlikely it was fix the problems in the priesthood or fill Roman seminaries with students again. In fact, it is rather offensive for the Pope now to claim it was a decision based upon greed. If that is the case, this would constitute a rather petty abuse of marriage at the hands of the Roman hierarchy.
If Rome were to change the discipline, it would require Rome to change many other disciplines or practices. These certainly include the housing, compensation, health insurance coverage, and retirement plans for Roman clergy. If it was not simply about money in the past, it could be about money now. How much would Rome be willing to change to allow the choice to marry to enjoy sanction as well as permission? Oddly enough, every married pastor knows that part of the difficulty of the vocation is balancing the personal with the parish. A wife and children do not quite make life easier even if they do make that life fuller. Curiously, however, non-Roman clergy who remain unmarried are often viewed with suspicion and find it harder to find a parish position the longer they remain unmarried. What is even more curious is that Pope Francis has a habit of off hand remarks that appear to indicate a change in Roman practice is forthcoming only to see that nothing happens but conflict and confusion. In that regard, Pope Francis is doing no one any service by demeaning the reason for the discipline while at the same time holding out little hope of a change.