From almost prehistoric times the Irish were skilled artificers in gold and bronze, and, at the advent of Christianity, had already evolved and perfected that unique system of geometrical ornament which is known as Celtic design. The original and essential features of this system consisted in the use of spirals and interlacing strapwork, but later on this type was developed by transforming the geometrical fret into a scheme of imaginary or nondescript animals, portions of which, such as the tails and ears, were prolonged and woven in exquisite fancy through the border. The artistic features of Celtic book decoration consist chiefly of initial letters of this nature embellished with color. Amongst the ancient Irish there was a keen knowledge of color and an exceptional appreciation of color values. Thus it was that in the early centuries of Christian Ireland the learned monks, transcribing the Gospels and longing to make the book beautiful, were able to bring to their task an artistic skill which was hereditary and almost instinctive. The colors which they used were mostly derived from mineral substances and the black was carbon, made, it is conjectured, from charred fish-bones; but with them was combined some gummy material which made them cling softly to the vellum and has held for us their lustre for more than a thousand years. It is noteworthy that neither gold nor silver was used for book decoration, and this would appear to be a deliberate avoidance of the glitter and glare which distinguish eastern art. _The Book of Durrow _(in the Library of Trinity College, Dublin) is the oldest specimen of Celtic illumination and, if not the work of St. Columcille, is certainly of as early a date. Each of the Gospels opens with a beautiful initial succeeded by letters of gradually diminishing size, and there are full page decorations embodying such subjects as the symbols of the Evangelists. The colors are rich and vivid and all the designs are of the purest and most Celtic character.