When George Augustus Robinson made his way through the green and blue-black wetland near Australia’s Lake Condah in 1841, the British-born builder encountered a sight that confounded his expectations of the land and of the Gunditjmara aboriginal people who lived there.

Robinson recounted “an immense piece of ground trenched and banked,” according to a 2017 story by the Conversation. From overhead, the system of fish traps and channels Robinson saw would have looked as long and winding as the eels caught in weirs and reed-woven baskets below. The channels were lined in basalt, the black rock formed from the lava that once oozed from a dormant volcano, and had been rearranged over the years as floodplains shifted. It was an ancient aquaculture system cultivated by the Gunditjmara, who used it to trap fish and eels, grow plants, and expand their population in the region now known as southwestern Victoria. The sophisticated system was effective and ancient, with its creation dating back before Stonehenge and the Great Pyramids.

“You don’t really see it anywhere else in Australia until European agriculture,” Ben Marwick, an associate professor of archaeology for the University of Washington, told The Washington Post. “It shows us they had a high level of technical skill, understanding of physics and of the natural environment.”

Not expecting such sophistication from the aboriginal people, Robinson marveled at the structures as “resembling the work of civilized man” — though his astonishment did nothing to stop European colonizers from killing the native people and destroying parts of the area with livestock and farming.

It would be more than a century before there would be any outside appreciation for the aquaculture system.