Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Synods of Sardica, Carthage, Constantinople, and Carthage Under St. Cyprian, Which Canons Were Received by the Council in Trullo and Ratified by II. Nice.: Canon LXXXIII

Canon LXXXIII.  (Greek lxxxvi.)

Of false Memories of Martyrs.

Item, it seemed good that the altars which have been set up here and there, in fields and by the wayside as Memories of Martyrs, in which no body nor reliques of martyrs can be proved to have been laid up, should be overturned by the bishops who rule over such places, if such a thing can be done.  But should this be impossible on account of the popular tumult it would arouse, the people should none the less be admonished not to frequent such places, and that those who believe rightly should be held bound by no superstition of the place.  And no memory of martyrs should at all be accepted, unless where there is found the body or some reliques, on which is declared traditionally and by good authority to have been originally his habitation, or possession, or the scene of his passion.  For altars which have been erected anywhere on account of dreams or inane quasi-revelations of certain people, should be in every way disapproved of.

Notes.

Ancient Epitome of Canon LXXXIII.

An altar in the fields or in a vineyard which lacks the reliques of the martyrs should be thrown down unless it would cause a public tumult to do so:  and the same is the case with such as have been set up on account of dreams and false revelations.

This is Canon xvij. of Carthage, September, a.d. 401.