The Vesica Piscis, and its name, is intimately connected with the discovery, by Augustus Caesar in the century preceding our Era, as narrated by Baronius, of a prophecy in one of the Sibylline books, foretelling "a great event coming to pass in the birth of One who should prove to be the true 'King of Kings,' and Augustus Caesar therefore dedicated an altar in his palace to this unknown God." Eusebius and St. Augustine inform us that the first letter of each line of the verses from the Erythrean Sibyl containing this prophecy, formed the word [Greek: ICHTHYS] (a fish), and were taken as representing the sentence: [Greek: Iesous Christos Theou Huios Soter]("Jesus Christ, the Son of God, the Saviour"). Based upon this discovery arose that extraordinary enthusiasm, during the second, third, and fourth centuries, for hunting up further prophecies in Pagan sources, resulting in a great number of Sibylline verses being invented, giving the minutest details in the Life of our Lord. These fabrications seem to have been at that time generally accepted by the masses as true prophecies, though we know now that they were written some centuries after the events they were supposed to foretell. Let us now return to the Vesica Piscis. In the paintings and sculptures of the Middle Ages, we find it constantly used to circumscribe the figure of the Saviour, especially whenever He is represented as judging the world and in His glorified state. Many beautiful examples of this in Anglo-Saxon work of the tenth century may be seen in King Edgar's Book of Grants to Winchester Cathedral and the famous Breviary of St. Ethelwolfe. Numerous illustrations of these and other pictures of the Middle Ages, as also diagrams of the properties of the Vesica Piscis, can be seen in the volume I have already referred to dealing fully with this subject. The building fraternity was a purely Christian community; the First Crusade raised a great enthusiasm for building Christian Churches, and brought in large gifts of money for that purpose. Up to 1140 Norman Architecture held sway, having the "Square" for its unit, its greatest symbol being the _Gnomon_, representing knowledge; but about that time, as we have seen, arose from the study of Geometry, the head of all learning, a Mystical form having the mysterious figure of the Vesica Piscis, the true Gothic Arch, with the Equilateral Triangle enclosed as its unit, and symbolising the Trinity in Unity. The recognition of the import of the Trinity was paramount throughout those early days; all important documents began with an Invocation of the _Tres Personae_, or were garnished with symbolic illustrations thereof; all the old MSS., already referred to, which have come down to us from that period, invariably commence with "In the name of the Father and of the Son and of the Holy Ghost."