Egyptian archaeologists announced Thursday that they had uncovered a massive, mysterious sarcophagus in the port city of Alexandria, according to CNN. A team uncovered both the 6-foot-tall black granite sarcophagus, said to be the largest in Alexandria’s history, and an unrecognizable alabaster bust during a routine sweep of a construction site on July 1. They have dated the site to between 30 and 305 BC, during Egypt’s Ptolemaic era. CNN also reports that unlike the many looted sarcophagi that have been found in the past, the intact mortar seal on this sarcophagi suggests that it has never been opened. As of Wednesday, archaeologists have not predicted what—or who—they’ll find inside.