Archaeologists and geologists have spent several centuries debating the origins of the materials that were used to construct Stonehenge, but the argument can finally be put to bed thanks to a new study in the journal Science Advances. Using an array of chemical analyses, the study authors provide pretty compelling evidence that the structure’s enormous boulders were sourced from a place called West Woods, some 25 kilometers (15.5 miles) away from the monument itself.

An iconic Neolithic landmark, Stonehenge is located in what is now the county of Wiltshire in the UK, and contains stones of various types and sizes. The primary architecture of the monument consists of enormous silcrete megaliths, commonly known as sarsens, while an array of smaller stones, called bluestones, are also found throughout the site. It is thought that the monument originally contained around 80 sarsens, though only 52 remain at the site today.

Previous research has traced many of the bluestones back to their various points of origin, with some having been transported over 200 kilometers (125 miles) from locations in Wales by the builders of Stonehenge.

The source of the sarsens, however, had until now eluded scientists, with much speculation but little real evidence regarding the origins of these colossal boulders. To finally solve the mystery, researchers used a technique called portable X-ray fluorescence spectrometry to analyze the chemical composition of the remaining sarsens, before comparing them with each other in order to determine their degree of chemical variability.

Of the 52 sarsens, 50 were found to share a consistent chemistry, indicating that they all came from the same place. To pinpoint this communal point of origin, the study authors compared the geochemical signature of one of these stones with those of other sarsens from around the UK. In doing so, they were able to identify West Woods – which lies to the north of Stonehenge – as the source of massive rocks.

While helping to solve one of the main mysteries surrounding Stonehenge, this finding also raises some fascinating new questions. For example, two of the sarsens included in this analysis – known as Stone 26 and Stone 160 – were found to have come from a different, unidentified point of origin, and the study authors are at a loss to explain this.

On the other hand, the results of this study do at least confirm that the other 50 sarsens were probably all brought to the site at the same time, suggesting that they were assembled during one phase of construction. This discredits a previous theory which stated that one of these sarsens, known as the Heel Stone, was sourced from nearby and erected first, and that the others were brought from afar at a later date.

In spite of the latest discoveries regarding Stonehenge’s history, scientists are still unable to confirm who built the ancient monument and what purpose it served.