Researchers have long been baffled at how the 4,500-year-old Giza pyramids could have been built with such intricate precision without the use of modern technology. For instance, one of the pyramids' biggest mysteries has to do with the remarkable alignment of the Great Pyramid of Giza, which is aligned almost perfectly along the cardinal points: north-south-east-west. Builders today would probably need to utilize computers, blueprints and perhaps even drones to achieve such precision.

"The builders of the Great Pyramid of Khufu aligned the great monument to the cardinal points with an accuracy of better than four minutes of arc, or one-fifteenth of one degree," wrote archaeologist Glen Dash, in a study published in the Journal of Ancient Egyptian Architecture.

It's impressive, close to perfect. But, as Dash also points out, not exactly perfect. In fact, the pyramids' alignments all suspiciously err to exactly the same degree. "All three pyramids exhibit the same manner of error; they are rotated slightly counterclockwise from the cardinal points," he added.

And this consistent error, Dash believes, might just provide the clue that finally solves the mystery of how these alignments were made. In fact, he and his team have devised a method that can achieve the same precision — and, tellingly, the same degree of error — found in the pyramids using nothing more than a simple rod-and-shadow trick.

The method, using just a rod and a string, relies on the shadows generated during the autumnal equinox, the moment when the plane of Earth's equator passes through the center of the sun's disc. The following illustration helps to demonstrate how it works:

Indian circle method The shadow line shown is typical of that formed in the summertime. In the wintertime, the shadow line curves away from the vertical rod. (Photo: Wilma Wetterstrom)

The equinox is important because that's when the tip of the shadow runs in a straight line and nearly perfectly east-west. Again, it's not exactly perfect; this method produces an error that is slightly counterclockwise — just like what we see with the pyramids' alignment.

And so, the thing that researchers have long-assumed must have been an immensely complicated engineering feat for the ancient Egyptians to accomplish might not have been so complicated after all. It's still pretty ingenious in its simplicity, however.

Of course, it's not currently possible to definitively prove that this was the method the Egyptians used, but it's certainly a compelling demonstration. It goes to show that even for our most intricate mysteries, we ought not overlook the simplest solutions.