On this day in 1980, one of the most mysterious monuments of our time was unveiled.

It’s known today as the Georgia Guidestones, and in all the years they’ve been in place we still haven’t learned much about what they’re for – or who put them there.

They stand in Elberton, in northeast Georgia, a town known for its many granite quarries.

One day in 1979, a man came to the Elberton Granite Finishing Company with extremely detailed plans for an enormous monument he wanted to build.

The company thought the idea wasn’t realistic, so they quoted the man an excessively high price to do the work.

But the man, who only gave the name R.C. Christian, told them he could pay any price they named, as long as he remained anonymous.

His identity has remained a secret for decades, and the stones were built as he’d requested.

There are five vertical slabs of granite reaching almost 20 feet high, with a smaller horizontal slab on top.

They’re arranged to align with solstices and equinoxes, sort of like Stonehenge.

And the slabs are inscribed with ten rules, in multiple languages, that claim to be “guidestones to an Age of Reason.”

Some are sort of New Agey, like “leave room for nature.”

Others are ominous, like the one that says the world’s population should remain below 500 million, way below the actual population.

There are lots of theories about the purpose of the stones.

One of the most widespread ideas is that the stones were supposed to guide survivors of some kind of apocalypse, like a massive solar event that wiped out all our electronics, or World War III.

Whatever the intended purpose, the practical purpose these days is tourism: the Georgia Guidestones bring people to Elberton for a firsthand look at a real-life mystery.

If you’re even a little familiar with visual art, you probably know about Jackson Pollock.

But do you know about Charles Pollock?

There were two painters in the family.

Jackson’s older brother Charles was also an accomplished artist.

A museum in Palm Beach, Florida is exhibiting both brothers’ paintings together for the first time.

Nobody Knows How to Interpret This Doomsday Stonehenge in Georgia (Smithsonian)

Jackson Pollock’s Older Brother Charles Was the Family’s First Artist. Now, an Exhibition Brings Their Work Together for the First Time (Artnet)

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Georgia Guidestones photo by Dina Eric via Flickr/Creative Commons