The pointed oval, or vesica, is the conventionalized form of the fish. Ecclesiastical seals are commonly made in this form. It represents in rude outline a fish before the fins and tail are added.
Vesica
It is thought by some that the Gothic or pointed arch is derived from this symbol, being simply the upper half of a vesica.
Other symbols of our Lord are formed from monograms of the sacred name, Jesus, and of His official title, Christ. These are used separately and also together. The earliest form of monogram of the sacred name, that often found on tombs of early Christians, is the symbol which is said to have appeared in a vision to the Emperor Constantine.
The story is related by Eusebius, the Bishop of Caesarea, who asserts that it was communicated to him by Constantine himself, who confirmed it with an oath. The story is this: Constantine, whose mind was wavering between Christianity and paganism, was on the eve of a great battle. Knowing that Maxentius, his enemy, was seeking the aid of magic and supernatural rites, and remembering also that his father, who had been well disposed to the Christians, had always prospered, while their persecutors failed, he determined to pray to Christ. While engaged with such thoughts he saw at mid-day a luminous figure in the heavens, with the words, "By this conquer." Both he and the whole army were struck with awe at the sight. At night Christ appeared to him in a dream, holding in His hand the same symbol, which He admonished him to place upon his standard, and assuring him of victory. This symbol Constantine substituted the next day for the old Roman eagle upon the standards and shields of his legions.
What the emperor saw, or fancied he saw, for it cannot be doubted that Constantine believed what he stated, was a symbol already in use among the Christians, and whose meaning he doubtless already knew. It is formed of the first two letters of the Greek word for Christ, CHRISTOS (Christos); the X (Chi) being equivalent to our Ch, and the P (Rho) the same as our R.
