Petrus Peregrinus, a 13th century French scholar, conducted early experiments with magnets and wrote the first treatise on their properties. He shaped a lodestone into a needle shape that would point directly towards the lodestone, demonstrating early concepts of magnetic poles. While guarding the besieged city of Lucera, he wrote a letter describing all that was known about magnetite at the time. Significant progress was made in the 1600s by William Gilbert, who realized through his experiments that the Earth itself acted as a giant magnet.