Ichthys, the fish

The fish is among the oldest signs of the Christians. Clement of Alexandria tells them what to cut on their signet rings: “And let our seals be either a dove, or a fish, or a ship scudding before the wind”. Augustine explains the name: the initial letters of the Greek words for Jesus Christ the Son of God, the Saviour “make the word” for fish, “in which word Christ is mystically understood”. We know of no period rule for drawing it, so the construction here is our own, and it is exact. It is the vesica of the first plate, its two arcs carried on past their crossing. The upright between the two centres is given, and circles of that opening about its ends meet at the nose and at the crossing; the upright, run on both ways, cuts them at their far ends. Swings of twice the opening about one centre and about the far end of the other circle give the level line through that other centre; each tail ends where its circle meets the level line through its own centre. The upper edge is swung about the lower centre and the lower edge about the upper, so they cross once and part again as the tail.