The ancient Egyptian civilization flourished along the banks of the Nile River, which supplied the waters that ensured a prosperous and lengthy agricultural vitality over the course of thousands of years. On the strength provided by this rich agricultural productivity, the Egyptian civilization was able to develop into one of the foremost and notable ancient empires, excelling in architecture (including the use of the ramp and the lever in construction), science, medicine (including the art of mummification), mathematics, writing (hieroglyphic script), art, engineering, stone masonry, irrigation techniques, and commerce. See also: Africa; Agricultural science (animal); Agricultural science (plant); Agriculture; Anthropology; Archeology; Architectural engineering; Inclined plane; Irrigation (agriculture); Lever; Masonry; Mathematics; Medicine; River; River engineering; Science; Scientific methods; Stone and stone products

The Aztecs were an indigenous group of Mesoamerican tribal peoples whose influence dominated that region between the fourteenth and early sixteenth centuries. They predominantly spoke a native language called Nahuatl, and they lived a nomadic existence prior to the twelfth century. See also: Agricultural science (plant); Agriculture; Bean; Corn; Domestication (anthropology); North America

The Babylonian civilization flourished from approximately 1900 to 539 BC in the central and southern regions of Mesopotamia (present-day Iraq), predominantly between the Euphrates and Tigris rivers. Before the rise of the Babylonians, the area was inhabited by the Sumerians in southeast Mesopotamia and the Akkadians in northwest Mesopotamia. Through a series of expansions and conquests undertaken by various dynastic kings, these two cultures were incorporated into the Babylonian empire, which eventually established control over many other kingdoms from ancient Persia to Syria and Palestine. Along with this political and geographical dominance, the cities of the Babylonian empire became rich centers of learning, especially in the areas of astronomy, astrology (including the division of the night sky into a zodiac of constellations), mathematics, and medicine. The most important city was Babylon, which was situated 88 kilometers (55 miles) southwest of modern-day Baghdad. Once famous for its impressive architectural marvels, including massive walls, ziggurats (pyramid-shaped temples built on platforms), and the Hanging Gardens of Babylon (considered to be one of the Seven Wonders of the Ancient World), few remains of this ancient city can be found today. In addition, it is likely that the biblical story of the Tower of Babel was based on an ancient Babylonian structure. See also: Anthropology; Archeoastronomy; Archeology; Architectural engineering; Astronomy; Mathematics; Medicine; Science; Scientific methods; Zodiac

The Incas were a group of native South American people who created an empire that was the largest civilization in the New World prior to the arrival of Columbus. The early Incas predominantly inhabited the highlands of the central Peruvian Andes. Cusco (also spelled Cuzco) was their capital city. The Incas were mostly pastoral prior to the fifteenth century. Over the course of the 1400s and early 1500s, the Inca rulers consolidated and expanded their power over other tribes, creating an empire that encompassed an area from present-day Colombia to Chile along most of the length of the Andes. The economy of the Inca empire was based on a unique form of taxed labor in which people were required to contribute part of their labor to the state. In addition, the Incas were masters of civil engineering. For instance, they built a vast expanse of roads and bridges that connected all regions of the empire. They also excelled in their creation of architectural enterprises, building vast administration centers and temples. The citadel complex of Machu Picchu is one of the finest examples of Inca architecture. See also: Civil engineering; South America

The adoption of silver currency for use in trade revolutionized the medieval economy across northwest Europe beginning in 660–670 CE. Researchers have sought to determine the origins of the coins' silver to help illuminate long-distance trade routes; periods of economic expansion and contraction; and how, where, and when the region began minting silver. A group of researchers from Cambridge University in England has recently used new, minimally invasive techniques to shed light on the geographical origins of the precious metal. The tests showed that Byzantine silver made up the earliest coins as their popularity grew. Only a century later, however, this source was overtaken by silver from a mine in Francia (roughly corresponding to modern-day France), under Charlemagne's control. See also: Archeology; Mining; Silver

The Phoenician civilization flourished along the eastern coastlines of the Mediterranean Sea (the present-day coasts of Syria, Lebanon, and northern Israel) from approximately 2000 BC to 500 BC. Organized as a loose confederation of independent city-states (including Byblos, Sidon, and Tyre), the Phoenicians were the preeminent maritime traders of their time. During the height of their civilization (1200–600 BC), the Phoenicians established trading posts and colonies throughout the Mediterranean region, including northern Africa, Sicily, and Spain. See also: Anthropology; Archeology; Earliest seafaring; Mediterranean Sea

Over the course of history, smallpox has been among the most feared diseases of humankind. Caused by the variola virus (a DNA-containing member of the Poxviridae family) and spread by transfer through respiratory droplets during face-to-face contact, smallpox is an acute infectious disease, involving widespread skin lesions, often resulting in disfiguring scars on the face, and frequently leading to blindness and even death in about 30% of cases. Fortunately, through a successful global vaccination program, the disease was declared eradicated in 1979. Historically, though, the smallpox virus has been in circulation among human populations for about 3000 years. Notably, signature smallpox-like rashes and pustules have been identified on ancient Egyptian mummies from the third century BCE, and accounts of the disease have survived in written documents from China, Japan, and India dating to the fourth century CE. However, there is no written evidence of smallpox's existence in Europe prior to about the 11th century CE, which is when Europeans began travel to and from the Middle East during the Crusades. It was not until the 13th century CE that written evidence suggested the likely presence of smallpox among people living in central and northern Europe. Now, however, using DNA-sequencing methods on human skeletal and dental remains, investigators have identified the smallpox virus in DNA recovered from 11 Viking-Age individuals who lived in northern Europe between 600 and 1050 CE. See also: Anthropology; Archeology; Dental anthropology; Deoxyribonucleic acid (DNA); DNA sequencing; Infectious disease; Molecular anthropology; Physical anthropology; Smallpox

The Sumerian civilization flourished from 4500 to 1750 BC in the southernmost region of Mesopotamia between the Euphrates and Tigris rivers (located in present-day southern Iraq). It was the earliest society to establish urban centers and city-states—among them, Eridu, Kish, Lagash, Nippur, Ur, and Uruk—and these became seats of exceptional inventiveness and cultural creativity. The most important innovations of the Sumerians included the first writing system (cuneiform), the first wheeled vehicles (and possibly the wheel itself), the potter’s wheel, the sailboat, the first legal codes of law (such as the Code of Ur-Nammu, from 2050 BC), and the first system for time measurement that divided a 24-hour day into 60-second minutes and 60-minute hours. The Sumerians were also responsible for tremendous agricultural advances, including the invention of the plow and the development of irrigation systems, intensive cultivation, and large-scale farming. See also: Agricultural science (animal); Agricultural science (plant); Agricultural soil and crop practices; Agriculture; Anthropology; Archeology; Domestication (anthropology); Irrigation (agriculture); Linguistics; Numbering systems; Phonetics; Time