Humans take first place when it comes to making permanent alterations to Earth’s terrain, but we aren’t the only species to make a mark with infrastructure. A new look at an 1868 map has revealed that beaver dams in Michigan have been holding strong for at least 150 years.

The map is the work of Lewis Henry Morgan, a railroad lawyer who also worked as an independent anthropologist and biologist. According to Atlas Obscura, Morgan first traveled to Michigan's Upper Peninsula in the late 1850s for his railroad work and started studying the beavers in what is now the city of Ishpeming, about 15 miles from Lake Superior. The resulting book, 1868’s The American Beaver and His Works, had a fold-out map that included 64 beaver dams and their ponds.

The American Beaver and His Works // Archive.org

It was Carol Johnston of South Dakota State University who realized the value in Morgan’s maps to modern ecologists. She created an updated version using aerial photos and compared the two, discovering that about 72 percent of the dams and ponds still exist. Only 18 of the spots disappeared in that time (some as a result of human interference), and at least one pond was actually bigger than it was on Morgan’s map. The study was published in Wetlands last year.

While not all of the dams are still in active use, the findings illustrate the remarkable engineering capabilities of the North American beaver. The fact that so many structures are still standing after all this time—and in light of the industrialization and occupation of the area—is truly impressive; the rodent architecture is even older than many of humankind’s most beloved structures, including, as many have noted, the Eiffel Tower.

“This constancy is evidence of the beaver’s resilience and a reminder that beaver works have been altering the North American landscape for centuries,” Johnston writes in the paper.

For more, check out Morgan’s work in full on the Internet Archive, which includes lovely passages like this one, marveling at how beavers build dams even though they don’t have to:

"As the dam is not an absolute necessity to the beaver for the maintenance of his life, his normal habitation being rather natural ponds and rivers, and burrows in their banks, it is, in itself considered, a remarkable fact that he should have voluntarily transferred himself, by means of dams and ponds of his own construction, from a natural to an artificial mode of life."

On that note, don’t forget that International Beaver Day is April 7. These guys deserve some serious praise.

[h/t Atlas Obscura]