The coffin, made from black granite, measures 8.7 feet (2.65 meters) in length and dates to the Ptolemaic period. Mostafa Waziri, secretary general of Egypt's Supreme Council of Antiquities, said the sarcophagus is "considered to be the largest to be discovered in Alexandria."
Some tabloid outlets and internet users breathlessly warned about the dangers of a possible curse should the coffin be opened.
It turns out the coffin was hiding three skeletons and an abundance of red liquid sewage that had leaked in through a crack.
One of the dead appears to have suffered a blow to the skull. The ministry says the remains likely belonged to military officers or soldiers, and not royalty as some had speculated.
Egypt Today provided live updates on the opening of the 2,000-year-old coffin. The news outlet reports the male skeletons will be studied to determine their ages and face shapes. The 30-ton sarcophagus will be lifted out and transferred to a military museum.
"The sarcophagus has been opened," Waziri said, "but we have not been hit by a curse."