People of many nations have treasured pearls for thousands of years. The Romans valued pearls so highly, they created a law forbidding anyone except people of high rank, from wearing them. European explorers in the New World found many tribes of indigenous peoples in North and South America wearing pearl adornments. In 1579, King Philip II of Spain received a pearl from his representatives in Panama that weighed 1250 grains. Julius Caesar was also a great admirer of pearls and gave one as a gift that was worth $150,000. Pearl is one gem that does not come from the earth. It is a gem that forms in molluscs (clams, oysters, mussels and such), which can be found in fresh and salt water. Pearls are formed when some sort of small foreign body, such as a grain of sand, or a small parasite, gets inside the mollusc and layers of pearly material form around it as a natural defense against these irritants. In a true pearl (not cultured) the layers build up like the layers of an onion, in concentric circles. Light reflecting from these overlapping layers creates a characteristic iridescent lustre, also known as the orient of pearl. The older the pearl is, the more numerous the layers are, and the larger the pearl is.