Directa Decretal

The Directa decretal was written by Pope Siricius in February AD 385. It took the form of a long letter to Spanish bishop Himerius of Tarragona replying to the bishop’s requests for directa on various subjects sent several months earlier to Pope Damasus I. It became the first of a series of documents published by the Magisterium that claimed apostolic origin for clerical celibacy and reminded ministers of the altar of the perpetual continence required of them.

It is known that the First Ecumenical Council which took place at Nicaea included in its legislation a discipline of the priesthood known as clerical 'continence' or celibacy. This was the requirement of all priests and bishops to refrain from sexual contact with their wives or with any other woman. Thus, for a married man to become a priest, his wife had to agree to abstain from all sexual relations. This discipline added to the legislation of various councils, particularly the Council of Elvira, the date of which cannot be determined with precision, but believed to have been in the first quarter of the fourth century, in Spain.

While priests of the East and West were required to refrain from all sexual contact by virtue of their presiding at sacrifices, it is obvious that this was an exceedingly difficult discipline to maintain. Just as the Levite priests of the Jewish Temple in Jerusalem had been required to abstain from sexual contact (in order to achieve ritual purity) merely for a lengthy period prior to the periodic performance of the sacrifices of the temple, so the priests of the Early Church were required by ecclesiastical law to abstain from sexual contact. However, Christian priests presided at the sacrifice of the Eucharist every Sunday as well as the annual feasts of the various martyrs. Thus, Christian priests were not afforded by the Christian calendar periods in which they could be sexually active with their wives.

...
Wikipedia