Azure Window, Gozo, Malta

New York's Brooklyn Bridge and China's Lupo Bridge areamazing feats of engineering, but many of the world's most awe-inspiring bridges were crafted by Mother Nature herself. Natural bridges and arches areformed by the natural, selective removal of rock, caused by processes of erosion, according to the Natural Arch and Bridge Society. Some of the stunning bridges and arches on this list were formed by the corrosive action of flowing rivers or ocean waves. Some were formed by the collapse of a cavern roof or have been eroded by weather. But just as nature produced these arched wonders, nature can also take them away. With continued erosion, many of these bridges and arches will eventually collapse and disappear.

The Azure Window in the Maltese island of Gozo features a table-like rock arch over the sea, and with its proximity to two other natural landmarks (the Inland Sea and Dwerja Bay), forms a trifecta for tourism in the area. Created thousands of years ago when two limestone caves collapsed, the Azure Window's stunning geography has been featured in movies such as Clash of the Titans and television shows such as Game of Thrones. Unfortunately, the arch of the Azure Window has been disintegrating. In 2012, a large piece of rock from the left side of the structure collapsed, and made the "window" larger, The Times of Malta reported. It is expected that the arch will crumble away completely within just a few years.

NEXT: The world's highest natural bridge

Rainbow Bridge National Monument, Utah

Considered the world's highest natural bridge (it stands at 299 feet), the Rainbow Bridge National Monument is located in the rugged, isolated canyons at the feet of the Navajo Mountain, and is administered by Glen Canyon National Recreation Area, in southern Utah. The rock formations which comprise Rainbow Bridge are hundreds of millions of years old, according to the National Park Service (NPS). The base is composed ofKayentaSandstone, reddish-brown sands andmud laid down by inland seas and shifting winds over 200 million years ago, while the bridge itself is composed of Navajo Sandstone. This slightly younger formation (about 200 million years old) was created as wave after wave of sand dunes were deposited over an extremely dry period which lasted millions of years. The existence of the bridge wasn't publicized to the public until 1909, after two exploration parties went searching for the legendary span. In 1910, President William Howard Taft used presidential proclamation to designate Rainbow Bridge National Monument.

NEXT: The most spectacular arch in the UK

Green Bridge of Wales, Pembrokeshire, Wales

Probably the most spectacular arch in the United Kingdom, the Green Bridge of Wales is approximately 80 feet high, according to the Natural Arch and Bridge Society. It was formed through the natural erosion of limestone. Due to coastal erosion and waves, the Green Bridge will eventually collapse.

NEXT: You can climb 800 steps to reach this arch

Moon Hill, China

Located in southern China's Guangxi region, Moon Hill is a hill with a natural arch and moon-shaped hole, the remains of what was once a limestone cave. With an elevation of 380 meters (around 984 feet), the hill is 230 meters (around 754 feet) in relative height and 410 meters (1,345 feet) in length, according to Cultural China. Viewed from different points and perspectives, the moon-shaped arch can take on different shapes--from full moon to crescent. In 1981, about 800 marble steps to the arch were built to give visitors easy access to the tourist attraction. The climb takes roughly 20 minutes.

NEXT: A natural bridge carved out by a river in France

Pont d'Arc, France

A large natural bridge near the town of Vallon-Pont-d'Arc in France, the Pont d'Arc measures 60m (about 196 ft) wide and 54m (177 ft) high. The bridge, originally part of a cave system, was carved out by the Ardeche River and softened by weathering until only the sturdier limestone arch remained. Today, the area is a popular spot for canoeing and kayaking. Nearby is the Chauvet-Pont-d'Arc Cave, which contains the earliest known paleolithic cave paintings--about 30,000 years old--and is featured in the Werner Herzog documentary, Cave of Forgotten Dreams.

NEXT: One of the most photographed landmarks in England

Durdle Door, England

Located in Dorset, England, the picturesque Durdle Door is a natural limestone arch and one of the most photographed landmarks in the Jurassic Coast. The rock arch in the sea was formed as a result of the softer rocks being eroded away behind the hard limestones, allowing the sea to punch through them, according to the Dorset, East Devon and the World Heritage Coast. Similar to many natural bridges and arches, the Durdle Door arch will eventually collapse to leave a sea stack. In April 2013, a section of cliffs near the arch collapseddue to wet weather followed by dry conditions, according to the BBC.

NEXT: An arch that dates back to the Paleolithic age

Arco Naturale, Italy

A natural arch on the east coast of the Italian island of Capri, the Arco Naturale dates back from the Paleolithic age and is actually the remains of a grotto, according to Lonely Planet's Naples & the Amalfi Coast Guide.

NEXT: A bridge that became an arch

London Arch, Australia

Up until 1990, this stunning sea arch in Port Campbell National Park in Australia was known as "London Bridge" (because of its resemblance to its namesake), a double-span, natural bridge, formed by a gradual process of erosion. In January of 1990, the arch closest to the shoreline collapsed, leaving two tourists stranded on the outer arch until they were rescued by helicopter, and the formation was renamed "London Arch."

NEXT: One of Chile's most beloved natural monuments

La Portada, Chile

One of 15 natural monuments considered a "protected area" of Chile, La Portada is a natural arch located about 18 km (11 mi) north of the port city of Antofagasta. Standing 140 ft high, the arch measures 75 ft wide and 230 ft long. It has a base of black andesite stone, around which are arranged marine sedimentary rocks, a stratum of yellowing sandstone, and layers of the remaining fossils of shells dating back 35 to 2 million years ago. All this was formed during a long process of marine erosion.

NEXT: A bridge once owned by Thomas Jefferson

Natural Bridge Virginia, Rockbridge County, Va.

Surrounded by the Blue Ridge Mountains, the Natural Bridge of Virginia is one the country's oldest tourist attractions, and serves as a significant portal to American history. This majestic stone monument was discovered by the Native American Monacan tribe, was once owned by Thomas Jefferson, surveyed by a young George Washington, and traversed by Civil War soldiers. With an arch measuring 215 ft and with a span of 90 ft, the Natural Bridge consists of horizontal limestone strata, and is the remains of the roof of a cave or tunnel through which the creek once flowed, according to its official website. It has been designated a Virginia Historic Landmark and a National Historic Landmark.

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