An international team of archeologists have discovered a massive tomb that belonged to one of ancient Egypt’s earliest pharaohs. However, the ruler’s identity remains a mystery—as do many details of his long-lost dynasty.

The burial chamber was uncovered at the base of a desert cliff almost 23 feet beneath Abydos, one of Egypt’s oldest cities about 300 miles south of Cairo and roughly six miles from the Nile River. Ancient Egyptian mythology held that Abydos served as the burial place for Osiris, god of the underworld. Many of history’s earliest pharaohs also chose to be interred there inside a sprawling royal necropolis near Anubis Mountain.