Baalbek, Lebanon, is the site of one of the most mysterious ruins of the Roman Empire, a monumental two-thousand-year-old temple to Jupiter that sits atop three thousand-ton stone blocks. (The pillars of Stonehenge weigh about a fortieth of that.) The blocks originated in a nearby limestone quarry, where a team from the German Archaeological Institute, in partnership with Jeanine Abdul Massih, of Lebanese University, recently discovered what they are calling the largest stone block from antiquity, weighing one thousand six hundred and fifty tons and matching those that support the temple. Its provenance is more shadowy than one might expect of a three-million-pound megalith. Nobody seems to know on whose orders it was cut, or why, or how it came to be abandoned.

Baalbek is named for Baal, the Phoenician deity, although the Romans knew the site by its Greek name, Heliopolis. The historian Dell Upton has noted the unusual lack of documentation regarding who might have commissioned, paid for, or designed the temple. For Upton, the site is a metaphor for the role of imaginative distortion in architectural history. In the absence of concrete information, he writes, Baalbek has become “a very accommodating screen upon which to project strikingly varied stories.” There are many local legends about the origin of the temple: Cain built it to hide from the wrath of God; giants built it, at Nimrod’s command, and it came to be called the Tower of Babel; Solomon built it, with djinns’ assistance, as a palace for the Queen of Sheba. (It is said that the reason some blocks were left in the quarry is that the djinns went on strike.)

Testimony to Baalbek’s flummoxing properties can be found in the 1860 diary of the Scottish traveller David Urquhart, whose mental capacities were “paralyzed” by “the impossibility of any solution.” Urquhart devotes several pages to the “riddles” posed by the giant stones—“so enormous, as to shut out every other thought, and yet to fill the mind only with trouble.” What, for example, was the point of cutting such enormous rocks? And why do it out there in the middle of nowhere, instead of in a capital or a port? Why were there no other sites that looked like Baalbek? And why had the work been abandoned midway? Urquhart concludes that the temple must have been built by contemporaries of Noah, using the same technological prowess that enabled the construction of the ark. Work was halted because of the flood, which swept away all the similar sites, leaving the enigma of Baalbek alone on the face of the earth.

Scholars today like to laugh at Urquhart, particularly at his alleged belief that mastodons transported the stones. (I didn’t see any reference to mastodons in his diary.) But archaeologists are still trying to solve the riddles that he posed. Margarete van Ess, a professor from the German Archaeological Institute, told me that the purpose of the investigation that turned up the new stone block was precisely to ascertain how the three temple blocks were transported, and why two others like them were left in the quarry. (One of these previously discovered megaliths, known as the Hajjar al-Hibla, or Stone of the Pregnant Woman, turned out to have a crack that would have impeded its transport.)

Van Ess added that the blocks were probably cut in much the same way as the masonry used in the Pont du Gard, a Roman aqueduct in southern France, with each piece split from a larger expanse of limestone along natural fissures between the rock strata. Too heavy to lift, the blocks would then have been dragged from the quarry, probably using a capstan, a kind of human-driven winch—though the possibility of a sledge is also under discussion.

According to van Ess, the temple of Jupiter was definitely built by the Romans, in at least four phases. Construction began around 15 B.C., when the region first became a Roman province; the last remodelling would have taken place at the beginning of the third century A.D. Some non-Roman features, including “water basins in front of the temple” and “very high altars,” suggest that the temple might have been used “for local religious traditions,” in addition to the Roman rites.

But perhaps the biggest mystery is the question of size. Nothing puzzles archaeologists so much as impracticality, and although the karst topography of Baalbek demands strong foundation stones, and although one big stone is easier to move than many smaller stones, the pillars holding up the temple’s podium, van Ess says, are bigger than they need to be. In fact, Baalbek is one of a series of ancient projects that are under rigorous study by the Germans for being unnecessarily large. Van Ess and her colleagues are currently working to determine “the border between a ‘normal’ but expensive project”—a palace, for example—and a “giant one.”

I decided not to ask van Ess about an alternative theory that was proposed by the late author Zechariah Sitchin: that the podium at Baalbek had to be big enough to serve as an intergalactic landing pad, as documented in the Epic of Gilgamesh. I have found that archaeologists are seldom receptive to the notion of ancient astronauts—although one could argue that, when the archaeologists went looking for answers, all they managed to find was an even bigger and more mysterious stone block.

I think that it must be the unknowability of Baalbek that Proust had in mind when he gave the fictional sea resort in “In Search of Lost Time” the name of Balbec. (According to the art historian Mary Bergstein, Proust would have known Baalbek as “one of the most photographed of all archaeological sites in the nineteenth century.”) Before visiting Balbec, young Marcel becomes obsessed by the name and by Swann’s description of the local architecture: “The church at Balbec, built in the twelfth and thirteenth centuries, still half Romanesque, is perhaps the most curious example of our Norman Gothic, and so singular! It’s almost Persian in style.” The church of Balbec, like the temple of Baalbek, is a monument to the mystery of place, to the synthesis of West and East, real and imaginary, present and past.

In recent months, archaeological research around the site has been blocked by clashes between Syrian militants, Lebanese Sunni, and the Shiite group Hezbollah. Two weeks ago, in Ras Baalbek, about twenty-five miles north of the temple of Jupiter, six Lebanese soldiers were ambushed and killed by Syrian gunmen. Last Sunday, Syrian refugee tents in the Baalbek region were set on fire. When I expressed surprise that excavations could continue under these circumstances, van Ess explained that the archaeologists left the site some time ago. The giant stone was discovered in June, during a “period of ‘silence’ ” in the fighting, though the team waited until December to make an announcement. It isn’t clear when the dig will resume.