What do you see when you picture Rome? The Colosseum, perhaps? Maybe the Pope waving from his Vatican window, or the marble statues decorating the grand Trevi Fountain? You likely don\u2019t imagine underground Rome, with its ancient layers of civilization. An archaeological lasagna is hidden beneath today\u2019s modern metropolis. Floods, fires, and Jenga-like construction have seen Rome\u2019s history sink lower and lower through the ages. There are walkable streets up to 30-meters down, whispering catacombs covered by famous landmarks, and eerie chapels, frozen in time under the busy streets. All the Roman ruins you can visit above ground \u2013 baths, markets, theaters, and stadiums \u2013 are also found buried beneath the seven hills of Rome. Many can be explored, if you know where to go. Listed below are some of the most interesting and haunting places down in the depths of underground Rome. These historical locations dotted around the city combine to form one enormous archaeological site. You can also find out what it\u2019s like to descend beneath the city every day as we speak to Aurora Mele tour guide at Vicus Caprarius (Trevi Fountain Underground), one of the most impressive subterranean sites in Rome. Discover Vicus Caprarius \u2013 Trevi Fountain Underground https:\/\/www.youtube.com\/watch?vwh3eglCM2NA In a city of more than 2,000 fountains, only one of Rome\u2019s urban water features is the subject of daydreams around the globe. The Trevi Fountain is 26 meters tall and 49 meters wide, and is the gushing centerpiece of Piazza di Trevi. The Baroque exterior visible today dates back to Nicola Salvi\u2019s Papally approved design of 1732, but the water of the fountain has been flowing since at least 19 BC. The spraying fontana marked the end of the Aqua Virgo aqueduct, a vital water source for the people of ancient Rome. The 22 km waterway is considered a marvel of hydraulic engineering \u2013 it still functions perfectly today, 2,000 years later. On a fruitful day, the fountain yields \u20ac3,000 in loose change, as gleefully superstitious tourists fling coins over their left shoulder into the water (the money is collected and donated to charity). These donations are made as a sweetener for fate, aimed at securing a future trip to the Eternal City. Who knows where you end up if you throw the money over the wrong shoulder.What many of the coin-tossing tourists don\u2019t know is that the most rewarding Trevi Fountain experience takes place nine meters beneath their feet. Vicus Caprarius, or Trevi Fountain Underground, is one of the best examples of underground Rome, a rediscovered relic of the Imperial Age. Commonly nicknamed City of Water, Vicus Caprarius was discovered during the renovation of the former Cinema Trevi in 1999. Construction was halted immediately when it became clear there was more than just rats and debris beneath the Trevi district. Underneath the world-famous Trevi Fountain there's a jewel of underground Rome Having cleared out the long-undisturbed earth and rubble, archaeologists excavated labyrinthine passages and foundations of the old Aqua Virgo aqueduct, as well as discovering a residential area dating back to the first century. The structure was originally an insula, a common type of housing for Rome\u2019s poorest communities. It\u2019s thought that around the fourth century, this building was converted into a mansion house for a noble family and decorated with frescoes and marble. The water that pumps out of Trevi Fountain flows along ancient masonry through this underground complex, and has done for millenia. The digging and chiseling also uncovered a whole load of interesting artifacts. A collection of bronze coins was found stowed in a wall cavity, which was thought to have been hastily stashed as Rome was falling during the Sack of the Vandals in 455 AD. The owner of the coins, which were of little value at the time, was seemingly never able to retrieve their small wealth. Pristine African pottery that was used for transporting olive oil, fragments of ornate sculpture, partial mosaics, and the famous bust of Alexander Helios can all be admired in the Trevi Fountain Underground Museum. A tip for enjoying the full Trevi Fountain experience: Go early to avoid the crowds, get your photos, and throw your euros into the water (don\u2019t be tempted to have a swim. You\u2019ll be fined, and you\u2019ll never look as good as Anita Ekberg anyway). Then, see the inner workings of the fountain and discover underground Rome at Vicus Caprarius. Meet your insider: Aurora Mele 1. So, Aurora, tell us about your role as a Vicus Caprarius guide. I welcome guests and accompany them downstairs into the Vicus Caprarius. I usually give a general introduction of its history to everyone or a more detailed guided tour for our most curious visitors. Our company also provides own guided tours, if requested. What I love the most about the role is that I get to meet new people every day! Each visitor\u2019s experience is unique, and I love to hear about their stories. I learn something new every day I\u2019m there \u2013 it can be either a new word in a foreign language, or some unknown or curious fact about the world.2. How important has the site been during Rome\u2019s history? Ancient Rome was divided into 14 Regiones, or neighborhoods. The site of Vicus Caprarius was included in the VII Regio, rising along the ancient Via Salaria Vetus. Together with Via Lata it was one of the two main roads in the district. The structures found in the Vicus Caprarius would suggest anticipation of the intensive urbanization process of the VII Regio (which dated back to Hadrian\u2019s time), and so Vicus Caprarius is one of the few witnesses we have left of the \u201cNew City\u201d project undertaken by Nero after the Great Fire of Rome in 64 AD. 3. As someone who knows the ruins inside out, if you had to pick three highlights, what would you feature?If I had to choose, I would definitely go for the stamped brick, which was found quite recently, as well as the little coins treasure and the cavaedium. 4. What is your favourite part of the ruins and why? It is definitely the water overflowing from the ancient walls. It\u2019s magnificent, the sound of it still flowing after 2,000 years. I see people react like kids when they see the water. Nobody expects that. You can still see how crystal clear the water actually is. The name Acque Virgo comes from the pureness of the water, but there is also a legend that says a virgin showed thirsty Roman soldiers where the spring source of the Acque Virgo was. 5. I bet they appreciated that! What do you consider the hidden gems of Vicus Caprarius? Which parts do you wish people would stop to appreciate more? In my opinion the millennial stratification of Rome and how the Aqua Virgo is part of all these different ages of Roman history. Photo by Anthony Majanlahti on Flickr 6. A lot of ancient artifacts have an interesting story behind them. Do you have a favorite \u201cstory\u201d from the ruins?My favorite story is the one about the little coins treasure. It is supposed to be the hard-earned money of a servant working in the mansion, hidden by its owner when they had to flee during the Sack of the Vandals. 7. Fascinating! Do you have any insider tips for first-time visitors? I think the Vicus Caprarius\u2019 utmost important feature is the water, so I suggest taking a moment to focus on the relaxing sound of overflowing water. 8. After 2,000 years, the ruins must be very delicate. How are they protected and maintained after all this time? The structures are always monitored and controlled. Humidity and ventilation are regulated 24 hours a day and based on the amount of visitors. Lorenzo, our archaeology director, has the task of checking the state of conservation constantly. 9. Sounds like an important job. So, are the Vicus Caprarius ruins completely excavated? Is there more to find? Even though the excavations works may have stopped now, our dedication to improving and exploring the Vicus Caprarius is endless. I\u2019m sure that there is always something else to find here. As far as we know now, no mysteries about the ruins still need to be solved. However, if we could keep on excavating around our building, there\u2019s no doubt more ancient structures and stories will be found. 10. Which other underground places in Rome would you suggest visiting? Do you think more will be discovered? I\u2019m sure that more will be discovered! In Rome it\u2019s not surprising that every time they excavate for construction reasons, such as for underground stations or the maintenance of roads, some new finds come up. For now we suggest visiting the Basilica di San Clemente.Curious to see more of this spectacular underground Rome sight? Give yourself a sneak peek with this virtual tour given by Aurora herself! 5 more must-see underground Rome sights 1. Basilica of San Clemente Photo by Randall Skeffington on Shutterstock One of the best places to experience Rome\u2019s Scooby Doo-style stacked sandwich of civilizations is at the Basilica of San Clemente. As its minor basilica status suggests, it isn\u2019t the largest or grandest religious site in the city, but it\u2019s arguably the most revealing of Rome\u2019s past. In 64 AD, the Great Fire of Rome razed much of the city to the ground. Close to the location of the modern-day Colosseum, an insula and a swanky villa would later be built on the ashes of a flame-grilled warehouse. It was here that the site\u2019s religious history began. Christianity around this time was outlawed. But, like so many banned pastimes, this only made it more exciting. The wealthy Roman owner of the villa was thought to be a Christian convert, and opened up his home so Christians could have secret prayer meetings.\u00a0\u00a0 At the beginning of the third century, the mysterious pagan cult of Mithras was thriving. In the adjacent insula\u2019s courtyard a Mithraeum was built to provide a place of worship for cult members, many of whom were Imperial soldiers. In 313 AD, the Edict of Milan was issued, legalizing Christianity and effectively marking the end of Mithras\u2019 hold in Rome. The villa and the Mithraeum were both filled in, and a brand-new Christian basilica dedicated to St Clemente was erected on top. It would flourish until 1084, when it was badly damaged by pesky Norman invaders and abandoned. The top layer of this religious pancake stack, the basilica you see today, was built early in the 12th century.Nowadays you can visit the charming basilica to see its original 12th-century artwork, and descend into its dank, old passageways to discover the remains of its predecessors.\u00a0 Visitors can stand in the ancient Mithraeum, where blood rituals and ceremonies would take place all that time ago. There\u2019s Mithraic iconography aplenty, including the wholesome image of God being born from a rock and sacrificing a bull. You can also explore the original fourth-century church and admire some of the oldest Christian frescoes in Rome. 2. Piazza Navona Underground \u2013 The Stadium of Domitian https:\/\/www.youtube.com\/watch?vlZMhYENpnkU Piazza Navona is a hugely popular spot in the center of Rome. Tourists flock to it, like selfie-stick-wielding moths to a flame of likes and comments. There are grand mansions and churches, charming fountains and monuments, and lines of restaurants selling overpriced pizza. Piazza literally means square in English. But if you stand in the middle of Piazza Navona, you\u2019ll soon notice its elongated horseshoe shape. It\u2019s almost as if something different was there before\u2026 you see where this is going. A few meters beneath the modern Roman surface of Piazza Navona are the remnants of an ancient arena, the Stadium of Domitian. This once 20,000-seater bowl was actually commissioned around the time the Colosseum was completed, and would be finished 10 years later. The stadium was built in honour of Emperor Domitian, who ruled Rome between 81-96 AD. Unlike the Colosseum, which was built exclusively for gladiatorial fighting; and the Circus Maximus, which was designed for chariot racing; the Stadium of Domitian mainly staged athletic exhibitions. There was blood sport, of course, including one discipline where the only hold barred was intentional eye gouging. But there were also celebratory games and Olympic-like competitions, with javelin, discus, running, long jump and boxing. The athletes competed in the nude, just like the liberal Greek Olympians of old.Romans inside the stadium (it was free to enter) would walk between pearly white arches, and pillars made of travertine marble. Marble-covered staircases would elevate them to the open viewing area. Those of humble heritage would make their way to the cheap seats up top, while the plush lower level was reserved for the nobility. Has much really changed?The Emperor had his own balcony, decorated with statues of the Gods who were positioned with their eyes to action.The Stadium of Domitian would be abandoned around the end of the fifth century, coinciding with the rise of Christianity. The games were considered too pagan, the fighting too cruel, the nudity too frequent.Since 2014, down in underground Rome, a small portion of the stadium, now a UNESCO World Heritage site, has been open to the public. Visitors can see the remains of original staircases and walkways, long stripped of their beautiful marble cladding. You\u2019re able to pore over priceless items found during the excavations, and detailed displays, including pictures of what the stadium would have looked like in Emperor Domitian\u2019s day. More recently, another part of the stadium has been opened to very limited numbers of visitors. This enables history lovers to explore a newly restored archaeological area under the \u00c9cole Fran\u00e7aise, to understand more fully the arrangement of the stadium. There you can also see layers of ruins from the Renaissance and the Middle Ages. 3. Domus Aurea \u2013 Emperor Nero's forgotten palace One of the grandest and most interesting sites in underground Rome is party-boy Emperor Nero\u2019s Domus Aurea. \u201cGrand\u201d doesn\u2019t quite do Nero\u2019s indulgent, unashamedly conspicuous, 300-room palace justice.When his residence fell victim to the Great Fire of Rome, he was one of the few people who could shrug and demand an army of workmen construct him another. It\u2019s fair to say that no expense was spared on the site, which covered an area of Palatine Hill and Esquiline Hill approximately 25 times bigger than the Colosseum. Located inside a vast park and boasting a giant man-made lake, the first-century palace had everything. The finest marble fittings, walls adorned with stunning mosaics, indoor waterfalls, and even a revolving dining room with a ceiling that endowed guests with fresh flowers and perfume \u2013 minimalism wasn\u2019t Nero\u2019s thing. The emperor\u2019s life of extravagance didn\u2019t endear him to Rome\u2019s upper classes. Faced with the prospect of being overthrown, he took his own life. The new emperor, Vespasian, made a concerted effort to distance himself from his excessive predecessor and stub out Nero\u2019s legacy. And so, Domus Aurea was abandoned and built over, and would be forgotten for centuries, until somebody stumbled upon it at the end of the 1500s. An unsuspecting Roman actually stumbled, falling through a hole into a grotto, and inadvertently rediscovered Nero\u2019s \u201cGolden House\u201d.Fantastical human and animal depictions decorated the walls, now known as grotesque art. All the prominent artists of the time would soon be abseiling in to take a look \u2013 Michelangelo, Casanova, and the Marquis de Sade.Nowadays, Domus Aurea is an active archaeological site, but you can don a hard hat and join an expert guide for a look around this wonder of underground Rome. See the remains of Nero\u2019s party mansion, and picture it in its former glory as you search out its almost-forgotten vaults and frescoes. 4. Catacombs of Callixtus As morbid a realization as it might be, there are catacombs full of skeletons all over Rome \u2013 hundreds of kilometers of underground cemeteries lying mostly undisturbed beneath the city. When he wasn\u2019t building himself extravagant palaces, Emperor Nero was known to enjoy a spot of Christian persecution. From the first century, worship and burials were often forced underground, something that continued even after the Christianity was legalized by the Edict of Milan. The Catacombs of St. Callixtus, or Catacombe di San Callisto, are some of the most important in Rome, as they provided what were designed to be eternal resting places for early popes and some famous Christian martyrs. Due to constant sacks and pillages in the Middle Ages, these remains were removed for their protection. The Crypt of the Popes, or the \u2018Little Vatican\u2019 as it\u2019s affectionately known, housed the remains of nine popes and other important Christian figures. There is also the Crypt of St. Cecilia, the patron saint of music, who was martyred in the third century by Emperor Severus Alexander. There are ancient symbols, inscriptions, and insignias everywhere, marking the area as extra holy. Almost 20 kilometers long, and consisting of four storeys, as many as half a million ordinary Christians are also entombed there. The only way to explore the Catacombs of St. Callixtus is via a guided tour. That\u2019s a good thing \u2013 who would explain the mysterious symbols carved into stone and talk you through the meaning of ancient frescoes otherwise? 5. Catacombs of Domitilla Not everyone in Rome was mean to the Christians in the early centuries. It\u2019s thought that the Catacombs of Domitilla were made possible by a noble Roman, Flavia Domitilla. To give you an idea of her status, her uncle was responsible for building the Colosseum. A pezzo grosso, as the Romans might say. Before being exiled to the island of Ventotene for converting to Christianity (we\u2019ll assume it was less paradisiacal than it is now), Flavia stuck it to the pagans and donated her considerable land to be used as a Christian burial site. It would go on to become the largest underground cemetery in Rome. The catacombs were the burial place of famous martyrs Achilleo and Nereo, soldiers who renounced the violence and bloodshed of their profession but were eventually killed during the persecution of Emperor Diocletian around 304 AD. Their unhappy end is remembered by intricate pillar carvings, in an apse that was built around their crypts by Pope Siricius later that century. What really sets the Catacombs of Domitilla apart from the 60 or so other catacombs in underground Rome is its fourth-century basilica. Dedicated to St. Petronilla, the sunken, semi-subterranean basilica has got to be one of the spookiest and most beautiful churches in the world. Take a guided tour of this 17km labyrinth, and you\u2019ll also get to feast your eyes upon well-preserved religious frescoes and depictions of bible stories, as an expert guide fills you in on the details we couldn\u2019t fit here. Has all that talk of the Eternal City got you planning your next trip? Check out these tips on visiting Rome on a budget.