The colour red goes back a long way, quite literally.

These hand paintings in the Cave of Maltravieso in Spain are about 65,000 years old. That's before modern humans were present in the region.

These were made by Neanderthals.

These paintings (along with most prehistoric cave art) were made from red ochre.

Other natural sources of red pigment include the mineral cinnabar, minium (also called red lead), the root of a plant known as dyer's madder, and small insects called cochineals.

Linguists have found that red was almost always the third named colour (after black & white) in nearly every language.

And traces of red powder have been discovered in Homo Erectus burial sites in China from at least 200,000 years before Homo Sapiens even emerged.

And, ever since, red has been present in the art of every civilisation on earth, from Ancient China to Ancient Greece and Egypt to the Olmec.

But why has it always been so popular?

Well, there's science to it. Red is the third colour we perceive after black and white, and it elicits strong physiological reactions, including elevated heart rate.

It has the longest wavelength, and is least diffused, of any colour; it can be seen from the greatest distance.

And then we need only look at where red occurs in nature to see why it has had, since time immemorial, such powerful connotations.

Blood and fire, two universal and elemental features of human existence, are both red. Sometimes good, sometimes bad, but always there...

In Ancient Rome red was associated with Mars, the God of War. Roman soldiers wore red tunics and had red shields, and generals had their faces painted red during triumphal processions.

(It was also the colour of one of the four Roman chariot racing teams...)

In Christian art red, the colour of blood, came to be associated with martyrs and all forms of sacrifice and compassion.

Jesus was often painted wearing red (as in Leonardo's Last Supper) and Mary too, while the Pope has also worn red robes for centuries.

Then again, as the science shows, red is the second most visible colour after yellow.

Choosing red draws the viewers' attention best in a painting or stained glass window. It makes sense to make the most important parts of an artwork red, then.

Beyond piety and martyrdom red has also long been a symbol of royalty, might, and majesty.

From Charlemagne to Napoleon Bonaparte, red has been the colour of choice for kings and emperors all around the world for as long as there have been kings and emperors.

That's also true in China, where red had a strong association with the emperors.

But its primary symbolism is of luck, joy, and prosperity. Hence why the traditional colour for a Chinese wedding dress is red.

While in Japan red had a primarily protective symbolism, and has thus been used to paint torii, the ceremonial gates at the entrance to Shinto shrines.

In Ancient Rome freed slaves were given a red cap, and this was revived during the French Revolution as a symbol of liberty.

Then, during the 19th century, red evolved into the colour of socialism. In the 20th century, of course, it became the colour of Communism.

Red has also long been associated with love and passion - both in a positive and negative way, whether as true romance or something more scandalous. And yet red is the colour of anger, too.

In both cases they are strong emotions (also characterised by physiological reactions).

Red is also deeply intertwined with the iconography of evil.

Hell is usually portrayed as a realm of flames, and though depictions of Satan as red are relatively recent, the Book of Revelations in the Bible does prophecise a red dragon to appear during the Apocalypse.

For many people red is a colour they will love or hate depending on the team they support, for in sport red is one of the two or three most common team colours.

More practically, red is usually (though not everywhere) the colour of danger.

Traffic lights, stop signs, warning signs, warning systems (e.g. "red alert"), red cards in sport... the list goes on. This makes scientific sense, at least, for the reasons mentioned earlier.

The prevalence of red in flags is a result of this whole matrix of symbolic heritage.

Strange that one colour can mean love and anger, piety and evil, compassion and war, protection and danger, royalty and revolution... what unites them?

They're all powerful ideas or feelings.