Coming soon - journey down the Danube with CGTN's in depth reporting experience

It has been a frontier and a highway, an opportunity and a threat, the site of some of Europe's oldest cultures and of its most modern problems.

The Danube is Europe's second longest river (after the Volga) and the world's most international.

Like all great rivers it has a charisma which evokes strong emotions, starting with jealousy over its origins.

Two German towns long disputed its source, but officially it rises at an ornate well in Donaueschingen in the Black Forest of southern Germany. 

When it reaches the Black Sea coast 2,860 kilometers later it's only 300 kilometers further south, so its overall direction is gently south of east.

But from its source, it first races past the Alps in an arc northeast then southwards again.

It's slowed and broadened by the time it kinks sharply south just before Budapest, then trends east again near the Croatian city of Vukovar.

As it squeezes between the Carpathian and Balkan mountains on the Serbian-Romanian border it narrows to 150 meters in the Iron Gates Gorge, which ends in the largest dam system on the river.

From there it relaxes again, widening, slowing and shallowing as it trends east and then finally north before splitting into three at the delta and merging into the Black Sea on the Romanian and Ukrainian coast.

By then, the Danube has passed through or bordered 10 countries, four national capitals – Vienna, Budapest, Bratislava and Belgrade – dozens of other cities and 62 dams.

That's its topology, determined by geology and gravity, but its human history flows in the opposite direction. 

More than 7,000 years ago, the Hamangia culture of the delta region produced some of the world's most striking and enigmatic neolithic art, the Vinča Culture on the Middle Danube some of the first ever writing.

The Danube was the frontier of the Western Roman Empire, the fate of which was sealed when the Goths crossed over in the fourth century.

From the 15th century, it provided the Ottoman navy with a route into the heart of Europe, supporting the Sultan's army of conquest.

For millennia, it has been used for trade, fishing, power, irrigation and drinking water.

Today, the Danube basin is home to 83 million people. It is polluted by agricultural runoff, industrial waste, sewage, plastics, cosmetics and antibiotics.

Dams cut off fish from their spawning grounds, lower water tables and drain precious wetlands. It is controlled and altered by human action for more than 80 percent of its length.

Some problems are worse in former Eastern bloc countries, others in the more developed Western ones.

Fourteen countries and the EU are signed up to the International Convention on the Protection of the Danube River, committed to managing it sustainably and equitably.

One of the world's great rivers, loved, exploited, powerful but vulnerable, is a test case for our ability to cooperate and to nurture, rather than destroy our natural environment.