The shells Morse spotted had been accumulating for millennia. During the early to middle Jomon period, roughly 4000 to 2500 BC, sea levels along Japan's Pacific coast ran five to six meters higher than they do today, and temperatures averaged about two degrees Celsius warmer. The Kanto region's coastline pushed much further inland, and the Jomon people -- Japan's prehistoric inhabitants -- built settlements along these ancient shores. They left behind shell middens: dense deposits of discarded mollusk shells mixed with animal bones, pottery fragments, stone tool flakes, and botanical material. These middens are archaeological treasure troves, layered records of diet, environment, and daily life spanning centuries. Most are found along the Pacific coast, but the Omori mound sat unusually close to what would become one of the most densely urban corridors on Earth.

Edward Sylvester Morse had come to Japan to study brachiopods -- small marine invertebrates -- not ancient civilizations. Born in Portland, Maine in 1838, he was a self-taught naturalist who never earned a college degree yet became one of the most respected scientists of his era. His arrival in Yokohama on June 18, 1877, was supposed to be about shellfish. Two days later, the train ride changed everything. Morse secured permission from Tokyo Imperial University to excavate the site, and he brought modern field techniques that Japan had never seen: systematic layer-by-layer digging, careful recording of finds in context, comparison with similar sites worldwide. He published his findings in both English and Japanese in 1879, including detailed analysis of the shells that revealed environmental changes over time. The report became the first scientific publication of the university's Science Department. Morse is now remembered as the "Father of Japanese archaeology."

For all his scientific rigor, Morse had one critical blind spot: he kept no detailed records of where, exactly, he had dug. Over the decades following the excavation, the precise location of the site became uncertain. In 1929, authorities identified a spot in the Oi neighborhood of Shinagawa and erected a stone monument reading "The Shell Mounds of Omori." But the following year, a rival site near Omori Station itself was identified and given its own monument. The two locations sit only about 300 meters apart. Given that the original midden was likely enormous, both may well be parts of the same deposit -- the Shinagawa site perhaps where Morse actually dug, the Omori site possibly what he first glimpsed from the train. Rather than settle the dispute, the Japanese government in 1955 designated both sites collectively as a National Historic Site, extending the protected area in 1986.

Today the Omori Shell Mounds sit in one of the most heavily urbanized landscapes on the planet. The railway line that carried Morse past the site in 1877 still runs, now as the Tokaido Main Line, one of Japan's busiest rail corridors. The ancient coastline where Jomon people harvested shellfish six thousand years ago is buried beneath apartment blocks, convenience stores, and station platforms. Yet the stone monuments remain, marking a place where the deep past breaks through the surface of modern Tokyo. The pottery Morse unearthed -- classified as late to final Jomon period ware -- still sits in the University of Tokyo's collection, physical proof that beneath the concrete and neon of the world's largest metropolitan area, there are layers of human history reaching back millennia. Every commuter passing through Omori Station rides over ground that once fed a civilization.