Second Council of Nicaea, Canon XX

That from henceforth, no double monastery shall be erected; and concerning the double monasteries already in existence.

We decree that from henceforth, no double monastery shall be erected; because this has become an offence and cause of complaint to many.  In the case of those persons who with the members of their family propose to leave the world and follow the monastic life, let the men go into a monastery for men, and the women into a monastery for women; for this is well-pleasing to God.  The double monasteries which are already in existence, shall observe the rule of our holy Father Basil, and shall be ordered by his precepts, monks and nuns shall not dwell together in the same monastery, for in thus living together adultery finds its occasion.  No monk shall have access to a nunnery; nor shall a nun be permitted to enter a monastery for the sake of conversing with anyone therein.  No monk shall sleep in a monastery for women, nor eat alone with a nun.^[544]  When food is brought by men to the canonesses, let the abbess accompanied by some one of the aged nuns, receive it outside the gates of the women’s monastery.  When a monk desires to see one of his kinswomen, who may be in the nunnery, let him converse with her in the presence of the abbess, and that in a very few words, and then let him speedily take his departure.

Source edition notes

[544] Bev.  Neither shall a nun eat alone.

Translation: Henry R. Percival, The Seven Ecumenical Councils, NPNF II.14 (1900), via CCEL.