Gaius Plinius Secundus, known in English as Pliny the Elder, was a Roman author, naturalist, scientist, naval and army commander of the early Roman Empire, procurator, and friend of the emperor Vespasian. Pliny wrote the encyclopedic Naturalis Historia, a thirty-seven-volume work covering a vast array of topics on human knowledge and the natural world, which became an editorial model for encyclopedias. He spent most of his spare time studying, writing, and investigating natural and geographic phenomena in the field.