Humankind has created some of the most incredible buildings, celebrated for their structural engineering and architectural design -- from the Eiffel Tower to the Golden Gate Bridge -- but perhaps even more remarkable are the temples, monuments, and once-thriving cities left behind by ancient civilizations. The reason these archaeological sites are of much fascination is that these individuals were able to construct such impressive places without the tools and advanced technology that we have now.

In fact, a few structures have puzzled researchers, and others have speculated whether other, highly intelligent lifeforms were responsible for the creation of some sites because of how advanced they are. However, the more obvious answer is that it was a lot of manpower, determination, and innovation, that lead to the creation of some of the most magnificent, forgotten ruins.

There were many early cultures, from the powerful ancient Romans to the Incas and Mayan civilizations, all of which have left behind structures that are still visited today. While Machu Picchu, the Inca city set in the Andes Mountains, is one of the more well-known sites and dates back to around 1450 AD, there are other monuments, like the ancient Mayan city Tikal, that are much older.

Below are 20 ruins which are still around today, at least partially, which were left behind by an ancient civilization.

20 Pumapunku Was Built By An Extremely Advanced Civilization Without Modern Tools

The name Pumapunku (or Puma Punku) is not the only thing that’s unusual about these ruins, which are believed to date back to 536 AD. Apparently, these ruins, which are located in a region of Bolivia, were created by an extremely advanced civilization. And according to Ancient Code, many are puzzled by how humans were able to create these structures without the tools or technology that we have today.

The reason some believe that man may not have been responsible for these structures is that the biggest stone block is estimated to weigh about 131 metric tons, and according to the publication, it is difficult to picture mankind transporting such massive stones from the quarries located between 10 to 100 km away.

19 Machu Picchu Was Left Untouched For Centuries After The Incas Abandoned It

One of the most visited sites in Peru is Machu Picchu, an Inca city set in the Andes Mountains. The construction of Machu Picchu is believed to have taken place around 1450AD, and according to WWF, it was designated a UNESCO World Heritage Site in 1983.

Lonely Planet notes that the city was never found by the conquering Spaniards, and was left untouched, and mostly forgotten until the 20th century. Now, the site is one of the most popular tourist destinations and a highlight for many during their travels to Peru.

18 The Giza Pyramids Are Remarkable Structures Created Without Modern Technology

There are three giant Giza Pyramids located on the Giza Plateau, and according to National Geographic, they date back 4, 500 years ago and are part of Egypt's Old Kingdom era.

There has been some speculation as to how these pyramids were constructed, without advanced technology, but the project is reported to have been started by Pharaoh Khufu around 2550 B.C., and it is his Great pyramid that is the largest. The second pyramid was created by Khufu's son, Pharaoh Khafre, and this was the same time that the Sphinx was built, and lastly, the third pyramid was created by Pharaoh Menkaure, around 2490 B.C.

17 The Moai Statues On Easter Island Are Expertly Carved From Volcanic Stone

Easter Island, or Rapa Nui, is an island off the coastline of Chile.

The island is a cultural and historical location, which was designated a UNESCO World Heritage Site in 1995. According to UNESCO, during the 10th to the 16th century, the island’s inhabitants (of Polynesian origin) carved massive stone monuments known as Moai from volcanic stone.

These man-made figures can be found across the island, and the site suggests that there are around 900 statues, which range in height from 2 meters to 20 meters.

16 The Colosseum Is One Of Rome's Most Recognizable Landmarks

The Colosseum is one of the landmarks in Rome, Italy, and according to History, the amphitheater was a gift to the Roman people by Emperor Vespasian. Construction is thought to have been started around A.D. 70-72 and was officially opened in A.D. 80, by Vespasian’s son, Titus, to host 100 days of games, which included gladiator fights.

According to Rome.net, the Colosseum was the greatest Roman amphitheater, and remained open for 500 years, accommodating 50,000 people who visited for entertainment purposes.

15 Teotihuacan Was Once One Of Mesoamerica’s Most Powerful Cities

Teotihuacan was built between the 1st and 7th centuries A.D., and according to UNESCO, it was once Mesoamerica’s most powerful cities.

Located just 50km from Mexico City, and designated a World Heritage Site in 1987, the reason this city is so impressive is because of its architecture, which includes multiple temples. Two pyramids are particularly noteworthy, and these are known as Pyramid of the Sun (which is the third largest pyramid in the world), and Pyramid of the Moon, Adventurous Miriam reports.

14 The Bagan Temples Were The Capital Of The Kingdom of Pagan

The Bagan Temples can be found in the Bagan Archaeological Zone in Myanmar and were built as a symbol of religious devotion, Go Myanmar reports. According to the publication, the area was the capital of the Kingdom of Pagan from the 9th to the 13th centuries, however, in the last 500 years many of the temples have been renovated which has produced mixed results.

According to Lonely Planet, Bagan has been affected by several earthquakes and in August of 2016, 400 temples were affected.

13 Angkor Wat Is A UNESCO Designated Site And An Architectural Marvel

Angkor Wat is an ancient temple complex in Cambodia, and according to Live Science, the name means “temple city.”

Built around A.D. 1113 and 1150, the temple and the surrounding areas of Angkor are a UNESCO World Heritage site. It is also an architectural marvel because according to Lonely Planet, the temple was constructed using stones from the holy mountain of Phnom Kulen, more than 50 km away, and this must have been a logistical nightmare. In fact, it’s believed that 300,000 workers and 6000 elephants worked on the build of Angkor Wat.

12 The Ancient Mayan City Of Tikal May Date Back To The 4th Century B.C.

Tikal is an ancient Mayan city located in the tropical rainforests of Guatemala, and out of all of the man-made structures on this list, it may be the oldest one. Some of the buildings in the city and ceremonial center are believed to date back to the 4th century B.C., according to History.

It was considered an important place for the Mayan Empire, from 200 to 900 A.D., and the publication notes that by 900 A.D. the Mayan Empire and the city were in decline -- affected by drought and diseases.

Tourism has become the primary reason to visit The Tikal National Park, History reports, and the site was designated a World Heritage Site in 1979.

11 Derinkuyu's Underground City Was Discovered Quite By Chance

A massive underground city known as Derinkuyu was found beneath a Byzantine-era fortress in Nevşehir, Turkey. The discovery was made quite by chance; it happened in 1963 when a Turkish man was reportedly making changes to his basement wall, and he came across the underground city, My Modern Met reports.

The city, which was carved into the volcanic rock, is believed to have housed 20,000 people at one time. While the city prospered in the early Byzantine period, the publication notes that it is believed to have been started by the Phrygians, in the 8th to 7th centuries BCE.

10 The City Of Chan Chan Is Being Threatened By Rainfall

Chan Chan was the capital of the Chimú kingdom (which lasted from A.D. 850 to around 1470), and according to Britannica, the city was the biggest in pre-Columbian America.

The city was constructed from adobe brick, and finished with mud and decorated with elaborate friezes, and the publication claims the ruins of Cha Chan remain in fairly good repair because there is not often rainfall in the area. However, in recent years that has changed, and Smithsonian claims torrential rains are slowly washing away the city.

9 The Church of Saint George Is A Monolithic Stone Monument Unlike Any Other

Lalibela is a town in the Amhara region of Ethiopia and is home to a series of ancient rock churches. According to The Guardian, the 11 monolithic stone churches were created in the 13th century under the rule of King Lalibela, and were carved out of the red volcanic rock hills.

The last church to be constructed was the Church of Saint George (also known as Bet Giyorgis), a free-standing church in the shape of a cross and located in a pit. It’s quite different from any other church, and according to Atlas Obscura, the Bet Giyorgis church is the most magnificent of all the rock churches.

8 Göbekli Tepe Is Believed To Be The World's Oldest Temple

Some believe that Southeastern Turkey’s Göbekli Tepe may have been the world’s first temple, and according to Smithsonian magazine, the site predates Stonehenge by 6, 000 years. The site consists of massive stones, which were carved by prehistoric people before they even had the tools to do so, and the publication notes that German archaeologist, Klaus Schmidt, who has been working on the archaeological site, believes that this is the world’s oldest temple.

Yet despite being an ancient temple, the ruins were only discovered in the ‘60s, Ranker notes.

7 Almost A Million People Visit Stonehenge Each Year

Stonehenge is yet another architectural marvel, because the oldest section of the monument is believed to date back around 5,000 years ago, while the stone circle was created in the late Neolithic period, English Heritage reports. Unlike Göbekli Tepe, Stonehenge, which is located in Southern England, is one of the most well-known prehistoric monuments, and according to History, nearly a million people visit the site every year.

Stonehenge became a UNESCO World Heritage Site since 1986, and one of the main reasons for its appeal is that the people of this time would not have had the modern technology that exists today to erect these gigantic stones.

6 The Ruined City Of Palenque Is An Important Archaeological Site

Palenque is an interesting lost city, abandoned by the Maya who built it, and first discovered by the outside world in 1567, National Geographic reports. According to the publication, that discovery was made by Father Pedro Lorenzo de la Nada, who named the ruins Palenque.

The site now serves as an important archaeological site visited by researchers who come here to learn more about the Maya culture. The site’s detailed epigraphs, in addition to the innovative architecture, make it invaluable.

5 Petra Was Also The Set Of An 'Indiana Jones' Film

When seeing photos of Petra, a now abandoned city located in Jordanian desert, it may look vaguely familiar, and that’s because Indiana Jones and the Last Crusade was filmed here. But this city is a lot more than a film set, and according to National Geographic, it was built during the Nabataean empire between 400 B.C. and A.D. 106.

Petra served as a trading post, and according to Visit Petra, it became a rich location thanks to the trade of frankincense, myrrh, and spices. The site claims much most of Petra was destroyed in the 4th Century A.D. and it was lost to the western world until the early 1800s when a Swiss explorer reportedly made his way there.

4 The Abu Simbel Temples Weren't Undiscovered By The Western World Until 1817

The Abu Simbel is the site of an impressive ancient temple complex carved into the sandstone cliff face of the west bank of the Nile in Egypt. According to Britannica, the two temples on the site were commissioned under the rule of Egyptian king Ramses II.

The temples were undiscovered by the world until 1813, when a Swiss researcher was, according to Ancient, led to the site by a young boy. He was unable to find anything but is believed to have told his friend, Giovanni Belzoni, the story, and it was Belzoni who excavated Abu Simbel in 1817.

3 Temple Of Hera Played An Important Part In The Olympic Games

The Temple of Hera is a temple in Ancient Olympia, which according to Greeka, was first built in wood in the 7th Century, but later replaced with stone. The temple was dedicated to the Greek goddess Hera (the wife of Zeus), and is believed to date back to 650 B.C.

Warwick claims that the temple fell into disuse after the last games were held at this location in 393 AD, and in the years that followed the temple became covered in 3 to 4 meters of mud, with the first excavations taking place in 1929, focusing on the temple of Zeus. Later, a more sizable excavation happened between 1875 and 1881.

2 The Ruins Of The Van Fortress Date Back To The Early Iron Age

Looking at a photo of Van Fortress (or Tushpa) you may be forgiven for thinking the massive stone fortification doesn’t look like much, but there is a reason this structure is so important. And according to UNESCO, this is because the site, overlooking the Van Lake, served as the main city of the Urartians, the founders of the Urartian Kingdom, between the ninth and sixth century B.C.

According to Ancient Origins, the ruins date back to the early Iron Age, and to reach them you must hike for an hour up, up the face of a hill that demands some level of physical fitness.

1 Newgrange Is A PreHistoric Monument Created By Stone Age Farmers

Ireland is a country that is rich in natural beauty, culture and history, but another reason to visit would be to see the prehistoric monument, Newgrange. Located in the Boyne Valley, Newgrange is a passage tomb that dates back 5,200 years, the Newgrange website reports. The site also notes that the structure was created by Stone Age farmers and the large circular mound measures 85 meters.

According to Knowth, the passage tomb would have taken more than 20 years to be built with over 300 workers. And because of the importance of this monument, it was assigned as a World Heritage Site in 1993.

References: Ancient Code, WWF, Lonely Planet, National Geographic, UNESCO, History, Rome.netLonely Planet, Britannica