Alcuin of York — on Rev 9:19 (COMMENTARY ON REVELATION)

“The power of the horses is in their mouths, and in their tails. By the mouth is represented the knowledge of teachers, and by the tail, which should be placed behind, temporal power. So their power is in their mouths and tails because their way of preaching is to persuade people of wrong things; but as they are sustained by temporal powers, they are exalted through the things that are behind. For their tails are like to serpents, and have heads: and with them they hurt. Here, inversely, wicked teachers are represented by the tails, and secular power by the heads. It is fitting to say that bad preachers are like serpents, because it is with the voice of the one whose hiss Eve was allured by that they advise bad things. Since it is with the support of powerful people that they violently bring many people to do forbidden things, it is right to say that they have heads, which, according to another translation, are called dragons' heads.”