One of the Ecumenical Councils decided that from that council on, all new bishops would be celibate. I believe it was in the Fifth or Sixth Century. The bishops that were married stayed married, but all new bishops would not be. One of the issues was inheritance.
It was the Council at Trullo (692 AD), which had two canons on the subject. Neither of the canons forbid the ordination of married men to the episcopacy but did require them to separate themselves from their wives and for both husband and wife to live in celibacy. It is important to note the reason given for this admitted deviation from Apostolic Canons and the Holy Scripture: nothing to do with theology, ecclesiology or dogma but merely order in the Church because many people were "scandalized" that the bishop and his wife lived as ordinary husband and wife--under one roof, raising a family and having sex. Also note that neither canon changes the formal marital status of the bishop; they just separate a man and his wife, which is indeed contrary to Apostolic Canon 5, 1 Timothy 3 and the Lord's own words in Matthew 19:6 "What therefore God hath joined together, let not man put asunder. "Canon XII.
Moreover this also has come to our knowledge, that in Africa and Libya and in other places the most God-beloved bishops in those parts do not refuse to live with their wives, even after consecration, thereby giving scandal and offence to the people. Since, therefore, it is our particular care that all things tend to the good of the flock placed in our hands and committed to us,—it has seemed good that henceforth nothing of the kind shall in any way occur. And we say this, not to abolish and overthrow what things were established of old by Apostolic authority, but as caring for the health of the people and their advance to better things, and lest the ecclesiastical state should suffer any reproach. For the divine Apostle says: “Do all to the glory of God, give none offence, neither to the Jews, nor to the Greeks, nor to the Church of God, even as I please all men in all things, not seeking mine own profit but the profit of many, that they may be saved. Be ye imitators of me even as I also am of Christ.” But if any shall have been observed to do such a thing, let him be deposed.
Ancient Epitome of Canon XII: Although it has been decreed that wives are not to be cast forth, nevertheless that we may counsel for the better, we give command that no one ordained a bishop shall any longer live with his wife.
Aristenus: The fifth Apostolic canon allows neither bishop, presbyter, nor deacon to cast forth his wife under pretext of piety; and assigns penalties for any that shall do so, and if he will not amend he is to be deposed. But this canon on the other hand does not permit a bishop even to live with his wife after his consecration. But by this change no contempt is meant to be poured out upon what had been established by Apostolic authority, but it was made through care for the people’s health and for leading on to better things, and for fear 371that the sacerdotal estate might suffer some wrong.
Van Espen: In the time of this canon [of the Apostles so called] not only presbyters and deacons, but bishops also, it is clear, were allowed by Eastern custom to have their wives; and Zonaras and Balsamon note that even until the Sixth Council, commonly called in Trullo, bishops were allowed to have their wives. But not only do they command [in this canon] that bishops after their consecration no longer have commerce with their own wives, but further, they prohibit them even to presume to live with them.
Zonaras: When the faith first was born and came forth into the world, the Apostles treated with greater softness and indulgence those who embraced the truth, which as yet was not scattered far and wide, nor did they exact from them perfection in all respects, but made great allowances for their weakness and for the inveterate force of the customs with which they were surrounded, both among the heathen and among the Jews. But now, when far and wide our religion has been propagated, more strenuous efforts were made to enforce those things which pertain to a higher and holier life, as our angelical worship increased day by day, and to insist on by law a life of continence to those who were elevated to the episcopate, so that not only they should abstain from their wives, but that they should have them no longer as bed-fellows; and not only that they no longer admit them as sharers of their bed, but they do not allow them even to stop under the same roof or in the house.Source: http://www.ccel.org/ccel/schaff/npnf214.xiv.iii.xiii.htmlCanon XLVIII.
The wife of him who is advanced to the Episcopal dignity, shall be separated from her husband by their mutual consent, and after his ordination and consecration to the episcopate she shall enter a monastery situated at a distance from the abode of the bishop, and there let her enjoy the bishop’s provision. And if she is deemed worthy she may be advanced to the dignity of a deaconess.
Ancient Epitome of Canon XLVIII: She who is separated from one about to be consecrated bishop, shall enter a monastery after his ordination, situated at a distance from the See city, and she shall be provided for by the bishop.Source: http://www.ccel.org/ccel/schaff/npnf214.xiv.iii.xlix.htmlSource links appended by moderator after receipt from poster -PtA