Atticus (Adewele Akinnouye-Agbaje) and Milo (Kit Harington) kick some ash in "Pompeii." Sony Pictures

The historical action movie "Pompeii," opening Friday in theaters, is actually two movies rolled into one. The first film is a standard-issue gladiator picture, with our hero Milo the Celt (Kit Harington) fighting his way through a procession of increasingly scary bad guys. Milo's adventures take place in the slave pits and arenas of Pompeii, the ancient Roman city that was famously buried in volcanic ash around 79 A.D.

The second movie kicks in about halfway through, when nearby Mount Vesuvius erupts in a spectacular display that provides all that historically accurate ash. Also: pillars of fire, rivers of lava, flaming boulders, several earthquakes and even a giant Mediterranean tidal wave. What began as a B-movie gladiator flick ends as a disaster picture of epic proportions, with eye-popping 3-D effects.

History nerds should enjoy all the big-budget production values detailing the ancient Roman Empire. Before the fiery destruction, the movie depicts life at the height of the Pax Romana era -- the period of relative peace after Rome's initial expansion and before its eventual decline.

Watch the corners of the frame in "Pompeii" and you can glean some interesting tidbits -- for instance, some colosseums had a kind of partial and primitive retractable roof for shading the VIPs. Here are 10 more details about the ancient Roman empire that you might not know.

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The deadly arena of Pompeii hosted gladiator games and the occasional riot.Sony Pictures

The amphitheater of Pompeii is among the oldest surviving pieces of ancient Roman architecture. As depicted in the film, the colosseum was made of stone and plaster -- same as the larger Roman Colosseum -- and was designed to safely facilitate the gathering of large crowds for sporting events. That didn't always work to calm the hooligans, though. The Roman historian Tacitus writes of a huge riot in 59 C.E., between the Pompeians and visitors from the neighboring city of Nuceria, that resulted in a ban on colosseum events for several years.

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Under the floor of a Roman villa in Vieux-la-Romaine, FranceWikimedia Commons

Rome's famous public baths and many private villas of the rich were heated by what's called a "hypocaust" system. The floor of the building was raised off the ground with pillars and the space below sealed off and insulated with ceramic tiles. Hot air from the furnace or fireplace was routed into the enclosed space beneath the floor, and sometimes into hollowed-out walls. A system of flues circulated the hot air and vented out the smoke.

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Pompeii aristocrat Severus (Jared Harris) sports a complicated toga.Sony Pictures

While the college toga party may be an egalitarian affair, in ancient Rome the toga couldn't be worn by just anyone. In fact, the toga was restricted to Roman citizens -- a status governed by a complex system of laws. Togas weren't just sheets, either. The material, usually wool, was semi-circular in shape and draped by way of a complex method of tucks and folds. In later years, particular patterns and colors signified specific ranks and functions in Roman society.

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The "bikini girls" mosaic is found in an ancient Roman villa near Piazza Armerina in Sicily.Wikimedia Commons

Romans seldom went commando under those togas. Both men and women wore a loincloth called a subligaculum, made from wool or linen, although silken undergarments were prized by the wealthy. Women also sometimes wore a kind of strapless proto-brassiere called a mamillare or strophium. It was common for younger women especially to bound their breasts tightly, sometimes with soft leather.

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Milo and Cassia (Emily Browning), post-eruptionSony Pictures

Ancient Rome continued the Greek practice of recruiting civil servants from the lower classes -- slaves, freedman and other citizens of low birth. The emperor Augustus divided the city into a system of regions and precincts, each with magistrates responsible for fire protection and a limited form of criminal justice. After a particularly devastating fire in the year 6 A.D., Augustus established a fire brigade of seven squads with 1,000 men in each.

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Romans enjoyed their board games, such as this one from the second century C.E.Wikimedia Commons

Even lower-class citizens in the towns and cities of Rome had leisure time unprecedented in the ancient world. Board and dice games were popular at all levels of society, including relatively sophisticated military strategy games that echoed the Roman cultural premium on warfare. Working from writings and archeological evidence, game scholars have been able to piece together the rules of such recreational diversions as The Game of Kings, The Game of Brigands and The Game of Twelve Markings.

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Tourists examine the aqueduct of Segovia in Spain.Wikimedia Commons

Rome's famed system of aqueducts brought fresh water into the city, which was piped into public bath houses and private homes, then circled back again to flush the city's extensive sewer system. Aqueduct maintenance was handled by an elite squad of trained workmen, and the system established in Rome was eventually replicated in most provincial cities. A constant source of trouble was the hacking of the aqueduct system by poorer citizens tapping into the water supply illegally.

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Wikipedia Commons

Perhaps even more complex than its water system, ancient Rome's tax system was an equally elaborate invention. Seemingly everything was potentially taxable under Roman law. The most infamous example? The Roman urine tax, which was applied to those merchants who purchased, yes, urine collected from the public latrines. (The urine had specific chemical uses in tanning and clothes laundering.) Roman historians recount a conversation between emperor Vespasian and his son Titus, in which Titus complained of the offensive nature of the tax. Vespasian held up a gold coin and declared: "Pecunia non olet." ("Money does not smell.")

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Pompeii debutantes Cassia and Ariadne (Jessica Lucas) check out the boys over a cup of wine.Wikimedia Commons

Wine was the alcoholic beverage of choice in ancient Rome, and considered so crucial to daily life that even the lowliest of slaves were issued wine rations. Pompeii was one of the key wine centers in all the Roman world, and one side effect of the Vesuvius eruption was a "wine famine" that caused a ripple effect across the empire. When Pompeii's wine stores were destroyed, panicked Romans replaced their grain fields with vineyards, prompting a subsequent food shortage. A glut of wine from all the new vineyards followed, further destabilizing the economy. Emperor Domitian finally had to issue an edict prohibiting new vineyards.

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Sony Pictures

Rome may not have fallen in a day, but Pompeii did -- literally. Archeological studies suggest that ash and volcanic debris began falling on the city around midday on Aug. 24, 79 C.E. On the morning of Aug. 25, heated gas from Mount Vesuvius had rolled in and asphyxiated any survivors. Pompeii -- a city of 15,000 to 20,000 people -- remained buried and largely preserved, under a 20-foot layer of pumice, for the next 17 centuries.