1. Church of the Nativity, Bethlehem, West Bank, Israel - 565AD
This historically-significant church still holds multiple church services each day and is said to mark the birthplace of Jesus of Nazareth.
2. St. Catherine's Monastery, Sinai Peninsula, Egypt - 565AD
This monastery has been a place of worship and retreat continuously since the 6th Century. It houses the site where Moses is said to have seen the Burning Bush, according to Christian tradition.
3. Hagia Sophia (Santa Sophia), Istanbul, Turkey 537AD
The Hagia Sophia is considered to be one of the greatest examples of Byzantine architecture in the world. It has been a cathedral, mosque, and a museum during the time since its construction.
4. Basilica of Santa Sabina, Rome, Italy - 432AD
This basilica has remained unchanged ever since it was constructed some 16 centuries ago. It is the oldest extant Roman basilica in the city of Rome.
5. Basilica of Constantine, Trier, Germany - Circa 300AD
This is the largest extant hall from antiquity in the world today. It is used as a Christian church.
6. Tower of Hercules, A Coruña, Spain - Circa 150AD
This magnificent lighthouse is still in use nearly 1,900 years after it was completed, guiding ships along Spain's Atlantic coast, which is notorious for shipwrecks. It is the oldest existing lighthouse in the world.
7. Castel Sant' Angelo, Rome, Italy - 139AD
This building has been a mausoleum, a castle, fortress, prison and museum during its lifetime. It was once the tallest building in Rome.
8. The Pantheon, Rome, Italy - 118-128AD
Originally built as a temple to Roman gods, the Pantheon was converted into a church in the 6th Century. It has been used for this purpose ever since.
9. The Colosseum, Rome, Italy - 70-80AD
The interior of the world-famous Colosseum, constructed to host gladiatorial spectacles, is still occasionally used for small cultural events.
10. Arena of Nîmes, Nîmes, France - 70AD
This arena is used to host pop concerts and has also been the venue for an annual music festival since 1997.
11. Pula Arena, Pula, Croatia - 68AD
Pula Arena has hosted many international musicians in recent times, such as Pavarotti, Bocelli, Alanis Morrissette, Elton John, Sting, and Tom Jones. Two ice hockey games were even held in the arena as recently as three years ago.
12. Verona Arena, Verona, Italy - 30AD
This arena, which seats 15,000 people in its modern configuration, will be 2,000 years old in 2030 and hosts over 500,000 opera-goers each year. It is the chosen venue for many pop and rock concerts.
13. Theater of Marcellus, Rome, Italy - 13BC
This theater was initially built to host dramatic and musical performances, however, it was later used as a fortress. A palazzo was built atop its ruins during the 16th Century. Now divided into apartments, it is still inhabited to this day.
14. Great Stupa, Sanchi, India - 200BC
The Great Stupa is the oldest stone structure in India. It is a place of Buddhist worship and pilgrimage.
15. Mahabodhi Temple, Bodh Gaya, India - 260BC
In Buddhist tradition, this temple is said to mark the spot where Buddha attained enlightenment. While the current structure dates back to the 6th Century, temples have stood on the site since 260BC.
Content Sources: Gizmodo, Quora