Precious stones have fascinated mankind for millennia. These glistening and colourful pieces of nature were centres of various legends and superstitions, used for healing and protection as well as signs of status and wealth. Since the dawn of Christianity, precious stones embarked on a journey where they were gradually cleansed from their Pagan past of being used as magical amulets and introduced into the world of Christian symbolism and allegory. They became ubiquitous on the most important sacred objects – from reliquaries and crosses to altars and ornate covers for the Holy Scriptures, they broadcasted the inner, spiritual value of these items through means that were easily understandable by everyone. Similarly, the visual prowess of precious stones was also utilized through mosaics or sparkling stained-glass windows, transforming entire sacred spaces into magnificent jewel-like visions of Heavenly Jerusalem. Whether real or represented in glass, precious stones were far more than mere decoration or a sign of profane wealth. As this book shows, at least for a moment they enabled medieval eyes to experience the vision of otherworldly beauty and preciousness, a true vision of the sacred.