With invaders from the seas threatening Vietnam, the gods asked the dragon to create a natural barrier to protect its people.

BBC: The perfect trip: Vietnam

Regulation is a natural barrier to market consolidation across borders, but a second force bears on securities markets in exactly the opposite way: technology.

FORBES: Why the world would be better off with one big stock market.

The bastion of its long-guarded independence is the mountain range known as Picos de Europa (the Peaks of Europe), a vast natural barrier sheltering the region from the south.

BBC: A culinary pilgrimage along the Way of St James

They built only on high ground, mostly left the river to its own devices, and relied on the wetlands as a natural barrier to buffer and deplete any incoming hurricanes.

ECONOMIST: The state of Russia

Derived from the Sanskrit root "bid, " which means "to divide, " the Vindhya traverses the center of the country from east to west, forcing a natural barrier between northern and southern India.

CNN: Center Cut

The owner, Veolia Environnement, one of the giants of the industry, has built an underground wall of similarly waterproof clay around the site which extends deep enough to reach the natural barrier below.

ECONOMIST: The charms of modern landfills

Although it is a natural inhabitant of the Great Barrier Reef, the crown-of-thorns has, in recent years, undergone several population explosions.

ECONOMIST: A new study puts numbers to the Great Barrier Reef��s decline

But today, a permanent dam barrier not the envisioned natural course of rapids is what keeps sea lamprey at bay.

WSJ: Real Rapids in Grand Rapids?

In addition, EPA's and USDA's relevant authorities cover a range of natural resources and their supporting ecosystems, including waters, sediments, barrier islands, wetlands, soils, land management, air resources, and drinking water supplies.

WHITEHOUSE: Executive Order -- Gulf Coast Ecosystem Restoration