Paper, invented in China in the second century A.C., first spread throughout Asia with the dissemination of Buddhism. In 751, paper was introduced to the Islamic world when Arab forces clashed with the Tang Dynasty at the Battle of Talas. The Caliph Harun al-Rashid built a paper mill in Baghdad that introduced paper-making to Egypt, North Africa and Spain, where paper finally reached Europe in the 12th and 13th centuries, writes Millward.

On the Silk Road, travelers carried paper documents that served as passports to cross nomadic lands or spend the night at a caravansary, a Silk Road oasis. But the most important function of paper along the Silk Road was that it was bound into texts and books that transmitted entirely new systems of thought, especially religion.

“It’s not a coincidence that Buddhism spread to China around the same time that paper became prevalent in the region,” says Wen. “Same with Manichaeism and Zoroastrianism. One of the central significances of the Silk Road is that it served as a channel for the spread of different ideas and cultural interactions, and much of that relied on paper.”

Ancient Egyptians knew all about the power of a smoky eye. Way back in 4000 B.C., they started making kohl to line their eyes by mixing soot with galena, a mineral with a metallic bluish, gray or black hue. In some ancient paintings, Egyptians are depicted wearing green eye makeup, a shade they achieved by mixing another mineral, malachite, with the galena. Both women and men wore kohl eye makeup in ancient Egypt. They believed it had healing properties, as well as the power to protect the wearer from the evil eye.

The word “democracy” comes from the Greek term demokratia, literally meaning “rule by the people.” The word—and the concept—was introduced in 507 B.C. by Cleisthenes, ruler of the Greek city-state of Athens. This form of popular government consisted of three separate institutions: the ekklesia, or Assembly, which wrote laws and dictated foreign policy; the boule, a council of representatives chosen from the different Athenian tribes; and the dikasteria, a popular court system. In practice, only a small minority of the Athenian population took part in this early form of democratic government, as participation was limited to male citizens over 18. Athens’ system of popular rule would last only until around 460 B.C. when an aristocracy began to emerge under the leadership of the general Pericles. However, the democratic ideals and processes that originated in ancient Greece have influenced politicians and governments ever since.

In 490 B.C., as the story goes, a Greek soldier ran from Marathon to Athens, a distance of just over 26 miles, to bring news of the Athenian victory over the Persians in the Battle of Marathon. After delivering his message, the soldier promptly died. Over the centuries, his story became conflated with that of another, more famous, Greek soldier: Pheidippides. Before the Battle of Marathon took place, Pheidippides ran from Athens to Sparta to warn other Greeks of the Persian invasion, reportedly covering some 250 kilometers of uneven terrain in only two days. Unfortunately, Sparta was in the middle of a religious celebration when he arrived, and the Spartans were unable to mobilize for war until it was too late; the battle was already over. The first modern marathon took place at the revived Olympic Games in Athens in 1896 and was won—fittingly—by a Greek runner, Spyridon Louis.

The frighteningly durable substance known as opus caementicium, or Roman concrete, first emerged some 2,100 years ago and would make possible the architectural frenzy that began with Augustus, the first Roman emperor, in 27 B.C. The Romans mixed limestone with volcanic ash to form a mortar, then packed this thick substance together with chunks of brick or volcanic tuff to form the basic material for roads, bridges, aqueducts, buildings and other structures—including such enduring behemoths as the Pantheon and the Colosseum. Today’s scientists have concluded that Roman concrete, though weaker than modern cement, is astonishingly long-lasting, remaining relatively intact even after centuries of exposure to seawater and other damaging elements.

The Acta Diurna (or “daily acts”), which first appeared around 131 B.C., served as a gazette of political and social happenings in ancient Rome. News of events such as military victories, gladiatorial bouts and other games, births and deaths and even human-interest stories were inscribed on metal or stone and posted in areas with heavy foot traffic, such as the Roman Forum. Later on, during the first consulship of Julius Caesar, the Acta Senatus began chronicling the activities of the Roman Senate. The Acta Diurna, which continued publication under the Roman Empire (after 27 B.C.), can be considered the prototype for the modern newspaper.

This all-important invention comes from the beans of the cacao tree, which was cultivated more than 3,000 years ago by the Maya, Aztec and Toltec peoples of ancient Mesoamerica. These civilizations used the tree’s fruit, the cocoa bean, to prepare a frothy beverage they considered an energy drink, mood enhancer and aphrodisiac all in one. The Maya worshiped the cacao tree as sacred, and cocoa beans grew so valuable they were used as currency. In the 16th century, Spanish conquistadores seeking gold and silver in the New World brought chocolate back to Europe with them, launching a craze that—let’s be honest—never really ended.

For all its importance, it may surprise you to learn that zero is a relatively recent concept in human history, though it still has its roots in ancient times. The idea to use a zero-like symbol as a placeholder—to show the difference between 10 and 100, for example, or to show the absence in one column of another number (e.g. 2015)—emerged sometime after 300 B.C., when the ancient Babylonians adapted the Sumerian counting system. Half a world away, in ancient Mesoamerica, the Maya came up with the idea of zero as a placeholder independently, around A.D. 350. They used it in their elaborate calendar systems, but like the Babylonians, didn’t really conceive of zero as a number in itself or use it in equations. The more complete vision of zero didn’t emerge until the 7th century in India, when the Hindu astronomer Brahmagupta wrote rules for using zero in mathematical operations and equations, introducing the concept that zero could be seen as a number of its own.