In the written record, the study of herbs dates back over 5,000 years to the Sumerians, who created clay tablets with lists of hundreds of medicinal plants (such as myrrh and opium). In 1500 B.C., the Ancient Egyptians wrote the Ebers Papyrus, which contains information on over 850 plant medicines, including garlic, juniper, cannabis, castor bean, aloe, and mandrake. In India, Ayurveda medicine has used many herbs such as turmeric possibly as early as 1900 BC. Sanskrit writings from around 1500 B.C., such as the Rig Veda, are some of the earliest available documents detailing the medical knowledge that formed the basis of the Ayurveda system. Many other herbs and minerals used in Ayurveda were later described by ancient Indian herbalists such as Charaka and Sushruta during the 1st millennium BC. The Sushruta Samhita attributed to Sushruta in the 6th century BC describes 700 medicinal plants, 64 preparations from mineral sources, and 57 preparations based on animal sources. The Chinese emperor Shen Nung is said to have written the first Chinese herbal, the Pen Tsao. The Pen Tsao lists 365 medicinal plants and their uses - including Ephedra (the shrub that introduced the drug ephedrine to modern medicine), hemp, and chaulmoogra (one of the first effective treatments for leprosy). Succeeding generations augmented on the Shennong Bencao Jing, as in the Yaoxing Lun (Treatise on the Nature of Medicinal Herbs), a 7th century Tang Dynasty treatise on herbal medicine. The earliest known Greek herbals were those of Diocles of Carystus, written during the 3rd century B.C, and one by Krateuas from the 1st century B.C. Only a few fragments of these works have survived intact, but from what remains scholars have noted that there is a large amount of overlap with the Egyptian herbals. Greek and Roman medicinal pra tices, as preserved in the writings of Hippocrates (e.g. De herbis et curis) and - especially - Galen (e.g. Therapeutics), provided the pattern for later western medicine. Sometime between 50 and 68 A.D., a Greek physician known as Pedanius Dioscorides wrote (commonly known by its Latin title De Materia Medica), a compendium of more than 600 plants, 35 animal products, and ninety minerals. De Materia Medica remained the authoritative reference of herbalism into the 17th century. Similarly important for herbalists and botanists of later centuries was Theophrastus' Historia Plantarum, written in the 4th century BC, which was the first systematization of the botanical world. Sumer (from Akkadian Sumeru; Sumerian ki-en-gir15, approximately "land of the civilized kings" or "native land"[note 1]) was an ancient civilization and historical region in southern Mesopotamia, modern Iraq, during the Chalcolithic and Early Bronze Age. Although the earliest historical records in the region do not go back much further than ca. 2900 BC, modern historians have asserted that Sumer was first settled between ca. 4500 and 4000 BC by a non-Semitic people who may or may not have spoken the Sumerian language (pointing to the names of cities, rivers, basic occupations, etc. as evidence). These conjectured, prehistoric people are now called "proto-Euphrateans" or "Ubaidians", and are theorized to have evolved from the Samarra culture of northern Mesopotamia (Assyria). The Ubaidians were the first civilizing force in Sumer, draining the marshes for agriculture, developing trade, and establishing industries, including weaving, leatherwork, metalwork, masonry, and pottery. However, some, such as Piotr Michalowski and Gerd Steiner, contest the idea of a Proto-Euphratean language or one substrate language.