Shatranj made its way via the expanding Islamic Arabian empire to Europe and the Byzantine empire.[11] Chess appeared in Southern Europe during the end of the first millennium, often introduced to new lands by conquering armies, such as the Norman Conquest of England.[12] Chess remained largely unpopular in Northern Europe but started gaining popularity as soon as figure pieces were introduced.[12] The sides are conventionally called White and Black. But, in earlier European chess writings, the sides were often called Red and Black because those were the commonly available colors of ink when handwriting drawing a chess game layout. In such layouts, each piece was represented by its name, often abbreviated (e.g. "ch'r" for French "chevalier" = "knight"). The social value attached to the game seen as a prestigious pastime associated with nobility and high culture is clear from the expensive and exquisitely made chessboards of the medieval era.[34] The popularity of chess in the Western courtly society peaked between the 12th and the 15th centuries.[35] The game found mention in the vernacular and Latin language literature throughout Europe, and many works were written on or about chess between the 12th and the 15th centuries.[35] Harold James Ruthven Murray divides the works into three distinct parts: the didactic works e.g. Alexander of Neckham's De scaccis (approx. 1180); works of morality like Liber de moribus hominum et officiis nobilium sive super ludo scacchorum (Book of the customs of men and the duties of nobles or the Book of Chess), written by Jacobus de Cessolis; and the works related to various chess problems, written largely after 1205 [35] Chess terms, like check, were used by authors as a metaphor for various situations.[36] Chess was soon incorporated into the knightly style of life in Europe.[37] Peter Alfonsi, in his work Disciplina Clericalis, listed chess among the seven skills that a good knight must acquire.[37] Chess also became a subject of art during this period, with caskets and pendants decorated in various chess forms.[38] Queen Margaret of England's green and red chess sets made of jasper and crystal symbolized chess's position in royal art treasures.[36] Kings Henry I, Henry II and Richard I of England were chess patrons.[9] Other monarchs who gained similar status were Alfonso X of Castile and Ivan IV of Russia.[9] Saint Peter Damian denounced the bishop of Florence in 1061 for playing chess even when aware of its evil effects on the society.[12] The bishop of Florence defended himself by declaring that chess involved skill and was therefore "unlike other games," and similar arguments followed in the coming centuries.[12] Two separate incidents in 13th century London involving men of Essex resorting to violence resulting in death as an outcome of playing chess further caused sensation and alarm.[12] The growing popularity of the game now associated with revelry and violence alarmed the Church.[12] The practice of playing chess for money became so widespread during the 13th century that Louis IX of France issued an ordinance against gambling in 1254.[34] This ordinance turned out to be unenforceable and was largely neglected by the common public, and even the courtly society, which continued to enjoy the now prohibited chess tournaments uninterrupted.[34]