Synod of Laodicea, Canon IX:
The members of the Church are not allowed to meet in the cemeteries, nor attend the so-called martyries of any of the heretics, for prayer or service; but such as so do, if they be communicants, shall be excommunicated for a time; but if they repent and confess that they have sinned they shall be received.
Balsamon: "As canon vi. forbids heretics to enter the house of God, so this canon forbids the faithful to go to the cemeteries of heretics, which are called by them "Martyries."...For in the days of the persecution, certain of the heretics, calling themselves Christians, suffered even to death, and hence those who shared their opinions called them "martyrs.""