Sarcophagus found. Contents unknown. ('No guessing, please.')

CAIRO — Jet black and glistening with mud, the giant granite sarcophagus sits at the bottom of a pit in the Egyptian city of Alexandria, perfectly sealed despite being 2,000 years old, prompting ever-wilder theories about what secrets might lie inside.

The discovery of the sarcophagus on a construction site last month was a rare find in Alexandria, a fabled port city where most traces of Egypt’s ancient civilizations have crumbled into the waves or lie buried beneath urban sprawl.

A contractor digging foundations for a building on Al Karmili Street spotted the gleam of the burial vessel, which measures nearly 9 feet by 5. Archaeologists continued the dig by hand and were excited to discover that the mortar seal around the heavy lid was entirely intact.

That is unusual: Centuries of plunder by treasure hunters and professional tomb raiders have spoiled many ancient Egyptian burial sites.

Speculation was rife about who, or what, may lie inside.

There are few clues. The Egyptian Ministry of Antiquities has dated the artifact to the rule of the Ptolemaic dynasty, the Greek royal family that reigned over Egypt for about three centuries following the death of Alexander the Great in 323 B.C.

The sarcophagus is unmarked, although a badly eroded alabaster bust found nearby might be a likeness of its occupant. Some officials have theorized that it could be a city nobleman or some other leading figure from the Ptolemaic period.

Twitter, of course, gave vent to some wackier theories, including predictions of doom if the box were opened.

Zahi Hawass, an Egyptologist and former antiquities minister known for his Indiana Jones-style hats, has suggested the find could bolster efforts to locate the tomb of Alexander the Great.

But officials poured cold water on the speculation, and some seemed downright exasperated by it.

“I’ve had calls about this all day,” said Mostafa Waziri, secretary-general of the government’s Supreme Council of Antiquities. “People are saying it might contain Alexander or Cleopatra or Ramses. They don’t know what they are talking about.”

Waziri said his ministry had excavated 10 other sealed sarcophaguses in Minya, south of Cairo, this year. Some contained mummies, others had beads, amulets or religious statues, he said.

“So what about this one?” he said. “It might be nothing special. We will only know when we open it.”

Egyptian officials have learned to be cautious about making sweeping predictions. Three years of excited speculation about a hidden chamber in the tomb of the boy pharaoh Tutankhamen, which some experts said could contain the remains of Queen Nefertiti, ended in disappointment in May when radar scans proved conclusively that there were no hidden cavities after all.

Otherwise, though, it has been a good year for discoveries in Egypt. Archaeologists have found a hidden network of tombs in Minya and a rare Greco-Roman temple in the western desert, while authorities have stepped up efforts to recover ancient treasures smuggled abroad.

In the past month alone, the Ministry of Antiquities has recovered nine precious items from France, including colored coffins and statues of cats, and a giant haul of smuggled antiquities was seized at an Italian port, including gold-plated mummy masks, wooden model boats and 21,660 coins.

Thousands of artifacts, including much of the Tutankhamen collection, have been transferred to the Grand Egyptian Museum, a $1 billion project being built near the Giza pyramids outside Cairo.

After years of uneven progress, construction is now proceeding apace, and Egyptian officials say the building should be completed by the end of 2018, with a public opening sometime next year. Officials say it will be the world’s largest museum devoted to a single civilization.

Whether the contents of the mysterious black sarcophagus in Alexandria find their way to the museum is likely to be determined in the coming days, Waziri said, when officials prize open its lid.

“If we find an inscription, it will be lovely. If we find the owner, even better,” he said. “But no guessing, please. Archaeology depends on evidence.”