At its height in the first and second centuries AD, the city of Rome probably held around a million people, a size no European city reached again until London around 1800. (Estimates vary widely.) Feeding, housing, watering and governing such a place was a feat, and the solutions Romans found left marks that still stand.

Homes and households

The rich lived in a domus, a house built around open courtyards. Most people in the city lived in insulae, crowded apartment blocks several stories high, with shops at street level and cheaper, smaller rooms higher up, where fire and collapse were constant dangers. Augustus limited their height to about 70 Roman feet.

The family was the basic unit of Roman society, and the law gave its head enormous power. The paterfamilias, the oldest living male of a family, held legal authority over his children and grandchildren, including in early law the power of life and death, though by imperial times this was restricted and rarely used. Adult sons could not own property in their own right while their father lived. Women's lives varied with wealth and era; elite women could inherit, manage estates and wield real influence, as the women of the imperial family did.

Patrons and clients

Roman society ran on personal ties. In the patron and client relationship, a powerful patron gave protection and help, and the client gave loyalty, votes and public support. Each morning clients gathered at a patron's house to greet him, and the size of the crowd displayed his standing. The system bound rich and poor together, but it also kept the poor dependent.

Bread and circuses

From the time of Gaius Gracchus the state sold grain cheaply to citizens living in Rome, and from 58 BC it gave grain free to a large list of recipients, about 200,000 men under Augustus. Emperors also paid for spectacle. Chariot races in the Circus Maximus drew enormous crowds, and the Colosseum, opened in AD 80, held about 50,000 spectators for gladiator fights and animal hunts. The satirist Juvenal sneered that the people who once handed out commands and consulships now longed for just two things, bread and games, usually rendered in English as bread and circuses. Critics then and now read the shows as bribery that turned citizens into spectators; others see in them a shared civic life, not so different from modern stadiums.

Roman law

Law was perhaps Rome's most lasting creation. Starting from the Twelve Tables, Roman law grew through statutes, the yearly edicts of the praetors (the magistrates in charge of justice), and the opinions of expert legal scholars called jurists. Romans distinguished the ius civile, law for citizens, from the ius gentium, law shared with all peoples, which grew out of cases involving foreigners and traders. Some jurists linked the ius gentium to a natural law grounded in reason. The great jurists of the second and third centuries, such as Gaius, Papinian and Ulpian, wrote works later collected under the emperor Justinian, and that collection became the basis of civil law in much of Europe and Latin America.

Engineering

Roman builders were practical innovators. Roman concrete mixed lime with volcanic ash, called pozzolana, so that it could set even underwater, which made harbors, vaults and domes possible. The Pantheon in Rome, rebuilt under Hadrian, still has the largest unreinforced concrete dome in the world. The rounded arch, used again and again, carried bridges and aqueducts. The Appian Way, begun in 312 BC, was the first great Roman road, and by the second century AD some 80,000 kilometers of paved highway linked the provinces, built for armies and then used by traders and travelers. Aqueducts brought water from hills many miles away down gentle slopes, mostly through underground channels rather than the famous arches.

Worked example: the water commissioner

In AD 97 the senator Sextus Julius Frontinus became curator of Rome's water supply, and he wrote a report on its nine aqueducts. He found that private users were tapping pipes illegally and that the official records were unreliable, so he measured the flows himself. He was proud of the system: "With such an array of indispensable structures carrying so many waters, compare, if you will, the idle Pyramids or the useless, though famous, works of the Greeks!" (translated by Clemens Herschel, 1899). Apply this level's ideas. The aqueducts were engineering, but also politics: free public fountains and baths were a gift from the state, like bread and games, while wealthy households paid for private connections and some simply stole. Frontinus's real contribution was administrative: careful measurement, public records and enforcement of the law. Good infrastructure depends on honest bookkeeping as much as on arches.