▲During the 1960s, Queensland, Australia had become known for UFO sightings and several circles were reportedly found in swamp reeds and canefields. In 1966, it was reported that a large circle was found in the reeds of a swamp at Tully, in Queensland.

▲Their revelation sparked a new wave of crop circles in the 1990s. In 2009, Smithsonian magazine wrote: "Since Bower and Chorley’s circles appeared, the geometric designs have escalated in scale and complexity, as each year teams of anonymous circle-makers lay honey traps for New Age tourists."

▲Various theories of their origin were proposed. Some thought that they were created by UFOs, others that they were created by an unknown form of energy, possibly paranormal.

▲It has been reported that similar sites occurred across Australia, including one at Tooligie Hill in South Australia in 1971, and one at Navarre in Victoria in September 1972.

▲In 1991, Doug Bower and Dave Chorley made headlines when they claimed that they started the phenomenon in 1978. They demonstrated how to make a crop circle with a plank of wood, rope, and a baseball cap fitted with a loop of wire to stay in a straight line.

▲In the 1980s, the number of reported circles exploded and the term "crop circles" became popularly known.

▲But not everyone is satisfied that crop circles are entirely made by humans. Physics World reports that biophysicists have interpreted swollen stalks as evidence that the crops were
exposed to microwaves during formation of the circles, leading to patented
techniques for accelerated crop growth.

▲The publication states that since then, crop circles have been reported worldwide in a multitude of crops. In southern England, which sees most activity, circle-makers concentrate on rapeseed, barley, and wheat fields.

▲In 1990, a group of researchers, who described themselves as "cerealogists," set out to solve the mystery of the circles. They camped out on a hillside in Wiltshire with heat, light, and sound detectors, in the hope of recording the creation of a crop circle by a UFO or another non-human force.

▲Operation Blackbird included collaboration with the BBC and the area was patrolled by officials from the Ministry of Defence. On the second night, the monitoring equipment recorded flashing orange lights in the adjacent field. The next morning, two large circles with parallel lines between were discovered.

▲But the history of crop circles is much older. It has been reported that in 1678, a series of circles in Hertfordshire was attributed to the devil because they appeared to be beyond human capabilities.

▲After Bower and Chorley's confession, there was a heated debate of those who believed the men were responsible, and others who insisted that not all of the circles were explained by their claim.

▲When researchers examined the circles, they found a board game and a wooden crucifix in the middle of one. Researcher Colin Andrews admitted that the flashing orange lights had probably been the heat signature of hoaxers.

▲Later research found that crop circles in the UK were not spread randomly. They tended to appear near roads, by populated areas, and close to monuments such as ancient stone circles at Stonehenge and Avebury.

▲The phenomenon entered the zeitgeist in the late 1980s, after the media reported crop circles in Hampshire and Wiltshire.

▲Colin Andrews told the press, "Somebody had a joke, but it has actually set our research back. We have a serious job to do. It is only funny for 60 seconds".

▲The identity of those responsible for disrupting Operation Blackbird has not been confirmed, but the event undermined the reputation of the "cerealogists".

▲It has been reported that conspiracy theorists suggested that the army perpetrated the hoax in an effort to undermine the credibility of the researchers.

▲Independent studies published in 1999 and 2001 reported evidence that crops had been exposed to radiation during the formation of patterns, leaving those who believe the circles are created by men with planks of wood perplexed.

▲Bower and Chorley reportedly claimed to be inspired by the 1960s Australian events. They claimed responsibility for all British circles made prior to 1987, and for more than 200 crop circles in 1978 to 1991.

▲Other occurrences have less mysterious origins. In 2002, crop circles were reported near Pike Lake in Saskatchewan, Canada. It was later verified that they were actually piles of manure dumped by a local farmer.

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Similarly, those Australian circles in the 1960s may have been the result of wallabies high on opium. The marsupials have been reported to get into poppy fields grown for medicine, overdose on the crops, and walk in circles.

▲Crop circles were ubiquitous in the 1980s and '90s, but have since seemed to disappear. Take a look at the history of the phenomenon.