The Great Pyramid of Giza is so seemingly well-built that explanations of how the ancient Egyptians constructed it over 4,500 years ago have been filled with controversy, confusion, and mysticism. And sometimes even aliens. However, according to a new study, the engineering behind it might not be as bang-on as we once thought.

The study by the Glen Dash Research Foundation and the Ancient Egypt Research Associates has discovered that the Great Pyramid doesn’t have a perfectly square base, with one particularly lopsided west-facing edge.

Engineer Glen Dash and Egyptologist Mark Lehner looked for the original edges to the 138-meter (455 feet) tall Great Pyramid of Giza, the largest of the three pyramids found in Giza, just across the River Nile from Egypt's capital, Cairo.

When it was first constructed, under the rule of Pharaoh Khufu, the pyramid was lined with a white limestone casing. Over the centuries, this outer casing was stripped for use in other building projects and left the pyramid how we see it now. Much of this outer edge is too damaged to be of any use, however, the researchers managed to pinpoint 84 points of the original boundary around the pyramid’s 920-meter (3,020 feet) periphery.

Using this data they plotted out the lengths of the pyramid's four sides. The east side measured between 230.295 to 230.373 meters (755.561 to 755.817 feet) in length. However, the west side was around 230.378 to 230.436 meters (755.833 and 756.024 feet). That means the west side could be more than 14 centimeters (5.5 inches) longer than the east.

So, not too bad considering it was built 4,500 years ago. As the researchers say in the study “The data show that the Egyptians possessed quite remarkable skills for their time… We can only speculate as to how the Egyptians could have laid out these lines with such precision using only the tools they had.”

[H/T: Live Science]