In July of 1843, a group of 20 European colonists in Australia set out on a murderous mission. Members of the Indigenous Brataualang group had killed the nephew of the Scottish pioneer Lachlan Macalister—possibly in retaliation for the deaths of several Aboriginal people—and the colonists wanted vengeance. They surrounded a waterhole at Warrigal Creek in Victoria and opened fire, killing between 60 to 150 Brataualang people. According to firsthand accounts of the incident, the pioneers shot and shot, until the water ran red with blood.

The massacre at Warrigal Creek is one of the largest and most violent killings of Aboriginal people by European settlers, but it is far from the only one. As the BBC reports, researchers at the University of Newcastle in Australia have created a comprehensive online map charting the many massacres that took place between the years of 1788— when the first British fleet arrived in Australia—and 1872. The project seeks to highlight the sheer scope of violence committed against Aboriginal people during Australia’s Frontier Wars, a long, often vicious conflict that pitted Indigenous groups against pioneers from Europe.

Presently, the map only records episodes along the country’s east coast. The region is sprinkled with small dots marking the sites where massacres occurred, and clicking on the dots takes users to a page with details about the incident: the number of people killed, the weapons used, the groups involved, the motive for the attack. To date, researchers have charted six massacres of colonists by Aboriginal clans. Indigenous groups, by contrast, were subjected to more than 150 attacks, which resulted in the deaths of about 6,000 people. “It would appear that almost every Aboriginal clan experienced massacre,” the researchers write on the map’s website.

The team behind the project defined “massacre” as an episode of violence that claimed the lives of six or more people who were “were relatively defenseless against the assault (such as being on foot and unarmed, while the attackers were on horseback with guns).” According to Calla Wahlquist of the Guardian, researchers only included attacks that were mentioned in multiple sources, which often meant that they had to piece together a picture of events based on fragmented accounts in colonial newspapers, settlers’ writings, and indigenous oral history.

“You might get a little reference to a hunting party going off somewhere in a colonial newspaper, and a few years later there might be an account from a settler of seeing their neighbor going over the hill, going shooting,” lead researcher Lyndall Ryan told Wahlquist. “You have got to put the evidence together bit by bit by bit. It’s painstaking work.”

In an interview with Julie Power of the Sydney Morning Herald, Ryan said that the massacres were often “very well planned, designed to eradicate the opposition." Colonists also took pains to conduct their attacks in secret, and few perpetrators were ever brought to justice. Wahlquist reports that only one group of European settlers was ever executed for crimes against Australian Aboriginal people. It was a particularly brutal incident, during which settlers drove a group of 28 Wererai people into a stockyard and committed such atrocities against them that their bodies were difficult to count.

Ryan told Wahlquist that many non-Indigenous Australians are not familiar with the extent of the violence perpetrated by the country’s early settlers. She hopes the map will lead to a “much wider acceptance that this was a feature of colonial Australia.”

Moving forward, the research team plans to expand the map, shedding further light on a bloody chapter in Australian history.