Twenty days after the former vision I saw another vision, brethren — a representation of the tribulation that is to come. I was going to a country house along the Campanian road. Now the house lay about ten furlongs from the public road. The district is one rarely traversed. And as I walked alone, I prayed the Lord to complete the revelations which He had made to me through His holy Church, that He might strengthen me, and give repentance to all His servants who were going astray, that His great and glorious name might be glorified because He vouchsafed to show me His marvels. And while I was glorifying Him and giving Him thanks, a voice, as it were, answered me, “Doubt not, Hermas;” and I began to think with myself, and to say, “What reason have I to doubt— I who have been established by the Lord, and who have seen such glorious sights?”
I advanced a little, brethren, and, lo! I see dust rising even to the heavens. I began to say to myself, “Are cattle approaching and raising the dust?” It was about a furlong's distance from me. And, lo! I see the dust rising more and more, so that I imagined that it was something sent from God. But the sun now shone out a little, and, lo! I see a mighty beast like a whale, and out of its mouth fiery locusts proceeded. But the size of that beast was about a hundred feet, and it had a head like an urn. I began to weep, and to call on the Lord to rescue me from it.
Then I remembered the word which I had heard, “Doubt not, O Hermas.” Clothed, therefore, my brethren, with faith in the Lord and remembering the great things which He had taught me, I boldly faced the beast. Now that beast came on with such noise and force, that it could itself have destroyed a city. I came near it, and the monstrous beast stretched itself out on the ground, and showed nothing but its tongue, and did not stir at all until I had passed by it. Now the beast had four colours on its head— black, then fiery and bloody, then golden, and lastly white.
Source: The Pastor (or "The Shepherd") (New Advent)