The Hanging Gardens of Babylon are one of the ancient Seven Wonders of the World. They are famously known for their extraordinary terraced gardens, which were said to have been built in the ancient city of Babylon, near present-day Baghdad, Iraq. Unlike the other options listed, the Hanging Gardens are specifically mentioned in historical records as a wonder due to their impressive engineering and beautiful layout. The St. Louis Arch and The Colosseum, while architecturally significant, belong to much later periods and locations. The Great Wall of China, though ancient and remarkable, is not part of the traditional list of the Seven Wonders.

The Colosseum, also known as the Flavian Amphitheatre, is located in Rome, Italy. It is an iconic symbol of Imperial Rome and is known for its massive structure and historical significance as a venue for gladiatorial contests and public spectacles. The Colosseum is one of the most famous tourist attractions in the world and a key monument that illustrates the architectural and engineering prowess of ancient Rome. Unlike the other cities listed, Rome is the only location that has been home to this ancient arena since its construction in the first century AD.

The Mausoleum of Halicarnassus was built as a tomb. The mausoleum was constructed in the ancient city of Halicarnassus (present-day Bodrum, Turkey) in the 4th century BC to serve as the final resting place for Mausolus, a Persian satrap. It was an impressive and grand structure, featuring intricate sculptures and architectural elements. The term "mausoleum" itself is derived from the name Mausolus, indicating its purpose as a tomb.

The correct answer is Mayans. Chichen Itza is an ancient Mayan city located in present-day Mexico. The Mayans were a Mesoamerican civilization known for their advanced knowledge in architecture, mathematics, and astronomy. Chichen Itza is one of the most important archaeological sites in Mexico and is famous for its pyramid, known as El Castillo or the Temple of Kukulcan. The Mayans built this impressive city between the 9th and 12th centuries, and it served as a political and economic center for their civilization.

The Great Pyramids of Giza are considered the oldest structure on the ancient list of the seven wonders. These pyramids were built around 2580-2560 BC and have stood the test of time, making them the oldest surviving structure from the ancient world. They were built as tombs for the pharaohs and are a testament to the advanced engineering and architectural skills of the ancient Egyptians. The pyramids continue to awe and inspire people from around the world with their grandeur and historical significance.

The Taj Mahal was built by a Mughal Emperor to honor his late wife. The Taj Mahal is a mausoleum located in Agra, India, and was commissioned by Emperor Shah Jahan in memory of his beloved wife, Mumtaz Mahal. It is considered one of the most beautiful and iconic buildings in the world and is a symbol of eternal love. The emperor wanted to create a monument that would be a fitting tribute to his wife and serve as her final resting place.

The Lighthouse of Alexandria was indeed a beacon for ships. It was one of the Seven Wonders of the Ancient World and was built to guide ships into the harbor of Alexandria, Egypt. Standing at a height of approximately 400 feet, it featured a fire at the top that could be seen from great distances, helping sailors navigate safely through the waters.

The Great Wall of China is indeed the longest man-made structure. It stretches over 13,000 miles and was built to protect China from invasions. The construction of the wall began in the 7th century BC and continued for several centuries. It is a remarkable feat of engineering and is considered one of the most iconic landmarks in the world.

Petra is the correct answer because it was discovered by a Swiss explorer in 1812. Located in present-day Jordan, Petra is an ancient city famous for its rock-cut architecture and intricate water system. It was established as the capital city of the Nabataeans, an Arab civilization, and was later abandoned and forgotten until its rediscovery in the early 19th century. The Swiss explorer Johann Ludwig Burckhardt is credited with bringing Petra to the attention of the Western world during his travels in the region.

The Statue of Zeus at Olympia, one of the ancient Seven Wonders of the World, was primarily made out of gold and ivory. It was crafted by the famed sculptor Phidias around 435 BC. The statue depicted Zeus seated on an elaborate throne, which included details and decorations made from precious materials. While the structure of the statue included a wooden framework to support the heavy materials, the visible parts that adorned this magnificent work were largely crafted from gold and ivory, showcasing the wealth and artistic achievements of ancient Greece. Steel and plastic were not materials used in that era, especially for such prestigious creations.