For what is now a yearly tradition, tens of thousands of people from all over the world gather on Salisbury Plain to watch the summer solstice sun rise and cast its glow on the Neolithic wonder that is Stonehenge. In fact, the spectacle is so awe-inspiring and impressive that a number of historians, archaeologists, and scholars suspect that the people who built it some 5000 years ago did so because of the annual astronomical event. Of course, with no written records, it’s impossible to know exactly how the site was used at the time, especially considering that the only surviving linteled stone circle in the world was built in 6 stages over 1500 years between 3000 BCE and 1520 BCE.
We know that the earliest dated structures discovered in the area are “four or five pits, three of which appear to have held large pine ‘totem-pole like’ posts erected in the Mesolithic period, between 8500 and 7000 BCE.” It was certainly unusual for hunter-gatherers of the age to build monuments, since there are no comparable known structures from this era in northwestern Europe. As such, we have no idea if and how these posts are related to the Stonehenge monument, which was gradually built up thousands of years later. The attractive and open landscape in the heavily forested area, however, may have been one of the reasons ancient peoples utilized the Salisbury Plain and eventually chose it to build Stonehenge.
But, there could be another, more substantial reason. Two types of stone were used at Stonehenge; the larger one is called sarsen and the smaller one is referred to as bluestone. Scientists assumed that the sarsen stones were brought from Marlborough Downs located 19 miles north of Stonehenge, and that the bluestones were obtained from the Preseli Hills situated over 150 miles away. Based on the large quantities of stone waste materials and broken hammerstones found in a field just north of Stonehenge, both types of stone were worked into shape after transport. There are, however, two sarsen stones that haven't been carved or shaped like the others — the Heel Stone and Stone 16.
Recent archaeological research shows that sarsen stones are found on the Salisbury Plain, though they tend to differ in size and shape. And even though many of the sarsen stones at Stonehenge were in-fact transported to their current locations, Stone 16, and the Heel Stone — which is located just outside the north-east entrance — may have already been there for millions of years. This is significant, because their lineup marks the horizon where the Sun rises on the summer solstice and sets on the winter solstice, which means “if the two stones were already sitting there, pointing at the solstice Sun, that could have given the site its significance for the people who lived nearby thousands of years ago.”
Without watches, it’s very difficult to tell time since the sun constantly shifts its rising and setting positions throughout the year. “In fact, the Sun only truly rises due east and sets due west on two days of each year, on both the Spring and Autumn Equinoxes.” So, for ancient cultures that relied on the observable patterns of the heavenly bodies, the equinoxes divided the year into two consistently reliable halves. Additionally, “the solstices mark the times in the year when the days are either at their longest or shortest, so the equinoxes are the midpoints between the longest and shortest days of the year.” Together, they divide the year into four easily trackable points, as the people who built Stonehenge probably knew.
According to Timothy Darvill, director of the Centre for Archaeology and Anthropology at Bournemouth University, people who lived approximately two miles away from Stonehenge constructed the oldest part of the monument around 3000 BCE. It consists of a circular ditch (330 feet in diameter) with an external low bank and an internal high bank. The enclosure had two entrances, a wide one to the north-east and a smaller one on the southern side, and 56 chalk pits called the Aubrey Holes — named after antiquarian John Aubrey (1626 - 1697) who first noted them in the 17th century — set around the internal bank. They may have initially held wooden posts, but recent research suggests that they were likely supporting Welsh bluestones later on.
But, it wasn’t until around 2600 BCE that another group began arranging the world-famous stones at the heart of the prehistoric monument. Over the next thousand years, “the sarsens were erected in two concentric arrangements” — an outer circle and an inner horseshoe made up of five trilithons — with the bluestones set up between them in a double arc. Around the same time, four Station Stones were placed “in a rectangular formation, aligned along the same solstitial axis as the great trilithon and the bluestone arc.” Sometime between “2030 and 1750 BCE, a ring of pits known as the Z Holes was dug outside the sarsen circle”; another ring “called the Y Holes, was added between 1640 and 1520 BCE.”
In 2015, Lloyd Matthews and Joan Rankin proposed that Stonehenge “was, in fact, a complex and significant prehistoric calendar.” First, they took a close look at its enclosure. “The circle is situated in such a way so that the sunrise positions of the Summer and Winter Solstices divide it neatly into two semi-circles.” They also found that the site’s 56 Aubrey Holes could have been used for keeping track of each passing day of the year and may have provided a way to track various astronomical cycles, all of which appear to commence from and — upon completion — reset to Aubrey Holes 28/27. As such, they concluded that “one end of the dividing line is the start of the yearly count and the other represents the finish of the year.”
So, there are 56 Aubrey holes in the circle. With posts in the holes, each space between two Aubrey Holes represents 1 day. To calculate 1 solar year, the day marker is moved around the circle 6 times in a counterclockwise direction, starting from the space between Aubrey Holes 28/27, totaling to 336 days (56 x 6 = 336). After 6 full revolutions, another “29 days are counted to day 365,” resulting in 1 solar year. In other words, 6.5 revolutions of the Aubrey Hole circle represents a year. Since the solar year actually lasts 365.25 days, 1 extra day compensates for the remaining .25 days. “Every 4 years the marker within the space representing the days remains at the end of the year for an additional 24 hours.”
Furthermore, out of the five tall trilithons at the heart of the enclosure, three appear to be marked. “Not only were the marks identified as intentional symbols carved into the stone face of Trilithons 52, 53 and 59, but faint traces on Trilithon 58 indicate that an expected fourth carving may well have existed.” The researchers discovered a strong relationship between the “various astronomical cycles and their end-positions on certain Aubrey Holes, the placement of the four Station Stones and the unusual Trilithon carvings.” In fact, it is highly probable that the symbol on Trilithon 58 “referred to the true end of the 33 year lunar cycle, 6 days after the 32 solar year cycle ends, and 6 Aubrey Hole counts (days) on from Trilithon 59.”
So, to sum up:
“The number 56 was significant because not only was it a manageable number in counting the 365 days of the solar year through 6 and a half revolutions; it was an evolution from splitting the year into two with the equinoxes; four with the addition of the solstices and eight with the Sun and Station Stones 91/93. It allowed the calendar year to start and end on the Summer Solstice in the right positions within the Aubrey Hole circle. Not only were the Aubrey Holes used as a yearly calendar and counter, they also provided a way to track various astronomical cycles, such as the 32 solar year cycle, the 33 lunar year cycle, and even for tracking the synodic periods of all the visible planets. This exploration of cycles within astronomical observances led to formal placement of the four Station Stones and the great trilithons.”
We may never know everything there is to know about Stonehenge, but we do have a lot of strong supporting evidence that the world-famous monument was an incredibly sophisticated and effective way of keeping track of time, the seasons, and the astronomical cycles in our solar system. And, we also know that the builders of Stonehenge were not the first to have tried to make sense of the sky patterns above them. Still, considering the beauty of a solstice sunrise on a bright summer morning, we can truly say that the builders of Stonehenge left us a stunning monument for the ages, and an ancient way to track them.