A morning drizzle eases and sunlight breaks through the clouds, its rays bouncing off puddles that have formed on the many blue tarps covering an excavation site. As if on cue, dozens of helmeted workers emerge with buckets, shovels and trowels in hand, heading off to their assigned corners for today’s dig.

Despite being smack dab in the middle of Tokyo’s Chiyoda Ward — and just across from the moat that encircles the Imperial Palace — the dig site is big: 7,700 square meters of prime real estate slated to be developed into a new residential highrise. For now, however, it’s where one of the largest excavations the city has seen in recent years is taking place, with remains that date back millennia unearthed by a team of archaeologists and part-time diggers.

“The soil has been layered over time, so the deeper you dig, the older the artifacts and ruins get,” says Shun Aiba, a researcher with Chiyoda Ward’s cultural properties section who is helping oversee the process.