For centuries, dyed fabrics ranked among the most desirable objects of the ancient world, fetching up to 20 times their weight in gold. Few people knew their complex secrets, carefully guarding the valuable knowledge. The Rarest Blue tells the incredible story of tekhelet, or hyacinth blue, the elusive sky-blue dye mentioned throughout the Hebrew Bible. Minoans discovered it; Phoenicians stole it; Roman emperors revered it; Cleopatra adored it; and Jews?obeying a Biblical commandment to affix a single thread of the radiant color to the corner of their garments?risked their lives for it. But with the fall of the Roman Empire, the technique vanished. Then in the nineteenth century, a marine biologist saw a fisherman"s shirt smeared with snail guts, marveling as the yellow stains turned sky blue. What was the secret? At the same time, a Hasidic master obsessed with the ancient technique posited that the source wasn"t a snail but a squid. Bitter fighting ensued until the chief rabbi of Ireland discovered that one of them was wrong. But had an unscrupulous chemist deliberately deceived him? Baruch Sterman brilliantly recounts the complete, amazing story of this sacred dye that changed the color of history.