Let's take a tour of the world in the year 16 CE.
The majority of the world's population live in a broad band stretching from Europe to the Middle East to India and then up to China. This is the region of organised states, cities, metalworking and literacy. The Roman Empire and China are the two strongest powers, and they are vaguely aware of each other through rumour and legend.
The Roman Empire dominates the Mediterranean. Ships loaded with grain sail regularly from Egypt to Italy to feed the immense urban population of Rome, the world's largest city. Spain, France, North Africa, Greece and the Balkans, Anatolia and the Levant are all firmly under Roman control. North of the Alps, Roman legions stand guard along the rivers Rhine and Danube.
Rome is currently under the control of the Emperor Tiberius, the reluctant successor to Augustus, the first emperor. His nephew Germanicus is currently leading a military expedition east of the Rhine to defeat the German tribes, though in the end no lasting results will come of this.
To the north of Rome are lands inhabited by Celts and Germans, classed as barbarians by the Romans. Britain and Ireland are home to dozens of small tribal kingdoms, as are Germany, Scandinavia and Eastern Europe. These peoples have not yet developed writing, so little is known of them except a few comments by Roman or Greek writers, and the material relics uncovered by archaeologists. They are an iron age culture, living in fortified towns and farming villages and ruled by a warrior aristocracy.
Further east, the steppes north of the Black Sea are controlled by the Sarmatians, a confederacy of nomad tribes whose power stretches from the mouth of the Danube to the Volga. They herd horses, live in tents and wagons, and use spears and arrows made with bone, because they do not have access to metal except through plunder or tribute. Their language is Indo-European, classed as 'Eastern Iranian'.
South of the Caucasus Mountains is the Parthian Empire, the one power bordering Rome that is strong enough to meet them head-on. Their ruling class is descended from nomadic horse archers, but about 150 years ago they conquered a large area of the Middle East. They see themselves as successors to both Alexander the Great and to the older Persian Empire. The capital of the Empire is Ctesiphon, just south of modern Baghdad, and their power stretches from the river Euphrates in Syria to the Indus, and from the Caspian Sea to the Persian Gulf.
Artabanus III is currently the King of Kings of Parthia - his coins use the Greek title Basileus Basileon, though it's a direct translation of the Persian Shahanshah. His realm is decentralised, with powerful princes ruling large areas of it, and he is currently engaged in a civil war with a relative called Vonones, son of a previous emperor.
South of Parthia is the Arabian Peninsula, a land of small trading towns and tribal kingdoms along the coast and Bedouin nomads wandering the interior. The Kingdom of Saba in modern-day Yemen and the Hadramite Kingdom to the east are the most powerful of several small realms in the region.
North-east of the Parthian Empire in Central Asia is the land of Tokharistan, established by the Kushans. They are a nomadic tribal confederacy from the steppes who conquered the former Hellenistic Greek nation of Bactria just over a century ago, and adopted many Greek institutions. Their power is currently centred in the modern-day nations of Afghanistan and Tajikistan, but in a few more years they will embark on a conquering spree that will end up extending the power of the Kushan Empire across northern India as far as the old Mauryan capital of Pataliputra (modern Patna) by the year 140 CE.
India itself is prosperous, but politically divided into many rival states.
In the north-west, the Gondopharid dynasty rules a powerful state from their capital at Taxila, near modern-day Rawalpindi in Pakistan. They are under Parthian influence, following the Zoroastrian religion. At their height the Gondopharids ruled a kingdom covering the whole Indus valley from the Punjab to the sea and stretching into Afghanistan, but by 16 CE they are in decline and about to be conquered by the Kushans.
The Saka or 'Indo-Scythian' people rule several kingdoms (or 'satrapies') in north-west India, including the areas of Mathura, Gujarat and Malwa. At this point in time many of them are formally and loosely subjects of the Gondopharid kingdom; they will later switch their allegiance to the Kushans. Many of their rulers are patrons of Buddhism.
The Ganges valley is currently the home to multiple small states, fought over by their neighbours.
To the south, the Satavahana kingdom is a powerful state with its capital at Pratishthana (modern Paithan in Maharashtra). At various points they dominate much of the Deccan and extend their power into the North Indian Plain, but at present they are under threat by the Saka. They encourage both Hinduism and Buddhism within their territory, and have trade links as far as the Roman Empire.
To the east, the coastal land of Kalinga under the Maha-meghavahana dynasty is a major mercantile power, conducting sea trade as far as Indonesia. In the southern tip of India, three kingdoms under the Pandya, Chola and Chera dynasties are also heavily engaged in ocean trade. The Anuradhapura kingdom rules Sri Lanka.
South-east Asia is currently undeveloped, without cities or organised states. The first kingdom in the region, known in Chinese records as Funan, will be created in the Mekong delta some time in the next hundred years. Indian artefacts, including a statue of the god Ganesha, have been found in Java and Sumatra from around this time too, indicating trade links that will eventually lead to the rise of civilisation in the region.
Chang'an (modern Xi'an) is the capital of China, the most populous state in the world with some 60 million people (Rome, the second largest state, has around 45 million at this time). The valley of the Yellow River in the north is still the centre of gravity of Chinese culture, but internal colonisation and construction of irrigation and flood-control works in the Yangtze valley are making that region increasingly important. Chinese military power extends as far as the Pearl River in the south, southern Manchuria and northern Korea in the north, and the Tarim Basin in the west.
China is currently under the rule of the bloodthirsty Wang Mang, the one and only emperor of the Xin dynasty. He was a Han official who seized power seven years earlier, and introduced radical measures to nationalise all land in the empire, abolish slavery, control prices through a state purchasing agency, introduce income tax, and create state monopolies over essential goods. His policies will become so unpopular that he will be overthrown in a revolt in another seven years' time, his body hacked to pieces, and the Han Dynasty restored.
Korea is controlled by multiple small realms which are being influenced by Chinese culture, responsible for the introduction of metalworking and Buddhism. The rise of the later Three Kingdoms, Goguryeo, Baekje and Silla, probably begins in this period, but the history is obscure.
Japan is the home of the Yayoi culture, hundreds of independent clans who have mastered the art of pottery and bronze-making, but do not yet have iron-working or writing. They are animists, following the religion that will later be codified as Shinto.
North of China, the steppes from Manchuria and Siberia through Mongolia to Xinjiang are dominated by the powerful Xiongnu confederacy of horse nomads. Ulei Hyan is the current Chanyu or ruler; his predecessors had declined in power and been forced into a tributary relationship with the Chinese emperors, but China's current difficulties due to Wang Mang will shortly give the Xiongnu the opportunity to reverse that power relationship and gain the upper hand.
Outside of the main civilisation belt, there are also isolated pockets of urban state societies in the Western Hemisphere, in Mesoamerica and the Andes.
In the Valley of Mexico, the city of Teotihuacan is perhaps the sixth largest in the world with a population of 125,000. Its culture, which includes pyramid-temples and human sacrifice, will have a lasting and widespread effect on the region; but unfortunately we know little or nothing about the people of the city, their form of government or the extent of their power. Even the name 'Teotihuacan' is not what they actually called themselves, but a name given by the Nahuatl-speaking colonists of the region nearly a thousand years later who were impressed by the vast ruins of the city.
Further south, the Mayan people have established a number of city-states, prominent among which is Tikal (though not yet at the size or power they will later achieve). One of their most notable achievements is the development of a system of writing — the only one in use in the Americas before the arrival of Europeans. The Maya cultivate maize, squash and beans, make pottery but not metal tools, and are ruled by a series of priest-kings in each city with no central authority.
There is also a developed society in South America in the Andes Mountains and the coastal plains of Peru. The Moche culture, based on the northern coast of Peru, constructs elaborate irrigation systems and monumental temples, and produces remarkable pottery artefacts (often of a very explicit sexual nature). Because they have not discovered the art of writing, little is known of their history or organisation, not even whether they were a single kingdom or a series of independent settlements. Their dating is also unclear: it's unknown to what extent their culture was in existence in 16 CE and how much would only emerge over the following centuries.
South of the Moche area is the Nazca culture. This is village-based and agricultural, but has also developed advanced pottery, textiles and irrigation systems. Their biggest claim to fame is the Nazca Lines, vast images hundreds of metres across created in the desert gravel.
Outside of these areas, very little is known about the population of North and South America at this time except what archaeology can uncover. It's believed the people are a mixture of small-scale agricultural communities and chiefdoms, and wandering hunter-gatherer bands; though well-enough organised in some areas to construct large earthworks. In North America the Hopewell culture maintains trade links along the rivers from the Great Lakes to the Mississippi and Ohio valleys, though it is not politically unified.
The same lack of knowledge also applies to Africa south of the Sahara. (Africa north of the Sahara is an integral part of the Mediterranean world and the Roman Empire.) The upper Nile valley and the Horn of Africa are relatively well-known because the states there are in trade contact with Egypt, Arabia and India; but West, Central and South Africa are isolated from the rest of the world by geographical barriers and distance. Camels have not yet been domesticated in Africa, limiting the possibility for travel across the Sahara.
The Kingdom of Kush, also known as Nubia, lies up the River Nile in modern Sudan. Its capital is the city of Meroë, 200 km north of modern Khartoum. Kushite culture and religion are heavily influenced by ancient Egypt, though relations between the two countries have not always been friendly. After Rome established control over Egypt, they fought a war againt Kush 38 years ago, and the kingdom is now in effect a Roman client state. Meroë is notable for its iron industry.
South-east of Kush is the Kingdom of Axum, in modern Ethiopia and Eritrea. In days to come it will grow into a powerful empire, but at present it is still quite small. The capital city, Axum itself, is inland, but the kings also control the port of Adulis (described as a 'fair-sized village') on the Red Sea, which exports ivory and other luxury goods to the Roman Empire and the kingdoms of western Asia. Culturally, Axum is closest to the people on the other side of the Red Sea in Arabia and the Levant. Surprisingly, the state religion is a form of Judaism, mixed with indigenous polytheistic traditions; Jewish missionaries, scholars and merchants are influential in Axumite society.
There are also a string of trading towns down the East African coast, mostly in modern Somalia but a few in modern Kenya and even as far south as Tanzania. A Greek description of the region states that "along this coast live men of piratical habits, very great in stature, and under separate chiefs for each place", but adds that the sea trade is in the hands of Arabs from the Yemen and Aden regions.
Inland, the broad belt of grassland and forest south of the Sahara is home to various peoples who have developed millet and rice farming and domesticated cattle. The town of Djenné-Djenno in modern Mali, though at this point still quite small, will become a centre of trade. Ironworking has also been developed in this region; the Nok people of modern Nigeria were prominent early users of iron, though archaeologists have discovered a scattering of sites that are probably earlier (though the exact dating is disputed).
A major social and political change affecting Africa in this period is the Bantu migration. Few details are known since the only evidence we have is linguistic and archaeological, but it seems that over the last few centuries a group of related peoples from West-Central Africa (the modern Nigeria and Cameroon regions) have gradually been expanding and colonising the rest of Central and Southern Africa. Their superior technology — millet and sorghum farming, yams and bananas, domesticated cattle, and in recent years iron tools and weapons as well — has allowed them to drive out the indigenous hunter-gatherer peoples and take their land. By 16 CE the Bantu people have spread in two directions from their original homeland: south down the coast past the Congo into Angola, and east to the region of Lakes Victoria and Tanganyika, from which they are currently expanding southwards. In the next few hundred years they will reach the southern tip of Africa.
Australia is inhabited by bands of hunter-gatherers, most of them semi-nomadic.
The Melanesian and Polynesian peoples have colonised many of the Pacific Islands, reaching as far as Fiji, Tonga and Samoa, However, at this point Hawaii and Easter Island have not yet been discovered.
Madagascar and New Zealand are probably uninhabited at this time; the last two major landmasses on Earth to be settled by humans (apart from Antarctica).