Metals are used in Northern Europe. Chinese record a comet. Building of the Great Pyramid of Giza (26th century BC). Sails used on ships (20th century BC). First ziggurats built in Sumer. Near East civilizations enter Bronze Age around 3000 BC. Oldest known medicine wheel constructed in the Americas. First Copper (~2500 BC) and then Bronze (~2000 BC) and other types of metallurgy are introduced to Ireland. Domestication of the horse with the coming of Indo-Europeans in central Eurasia. The chariot emerges in Eurasian Steppe just before 2000 BC. The camel (dromedary) domesticated (though widespread use took until mid-to-late 2nd millennium BC). Indoor plumbing and sewage in the Indus Valley civilization. Sumerian medicine discovers the healing qualities of mineral springs. Weaving loom known in Europe. Ornamental buttons—made from seashell—were used in the Indus Valley civilisation for ornamental purposes by 2000 BCE. Sumerian numerical system based on multiples of 6 and 12. Egyptians begin use of papyrus. Austronesian peoples have developed lateen sail, and the out-rigger as well as extensive development of celestial navigation systems. Oldest known evidence of the inhalation of cannabis smoke, as indicated by charred cannabis seeds found in a ritual brazier at a burial site in present-day Romania. Cultural landmarks c. 3000 BC–2500 BC: Tomb, Newgrange, Ireland, was built. c. 2750 BC–1500 BC: Stonehenge, Salisbury Plain, Wiltshire, England, is built. Completion of the Great Pyramid of Giza. Completion of first phase of Stonehenge monument in England. Era of Buena Vista pyramid/observatory in Peru. The Sydney rock engravings in Sydney, Australia, which are examples of Aboriginal rock art, date from around 3000 BC. Centuries and Decades References -97