Armed with machetes and chain-saws, hacking through fallen trees and wading through dense scrub, the archaeologists cleared a path down rocky trails.

At last, they reached their destination in Mexico’s Yucatán Peninsula: a hidden city where pyramids and palaces rose above crowds over 1,000 years ago, with a ball court and terraces now buried and overgrown.

Mexico’s National Institute of Anthropology and History hailed their work late last month, saying they had discovered an ancient Maya city in “a vast area practically unknown to archaeology.”

“These stories about ‘lost cities in the jungle’ — very often these things are quite minor or being spun by journalists,” said Simon Martin, a political anthropologist who was not involved in the work. “But this is much closer to the real deal.”

The team of archaeologists who discovered the ruins named them Ocomtún, using the Yucatec Maya word for the stone columns found around the ancient city.

The Mexican institute described the site, in Campeche State, as having once been a major center of Maya life. During at least part of the Classic Maya era — around 250 to 900 A.D. — it was a well populated area. Today it is part of a large ecological preserve where vines and tropical trees snarl boots and tires, and fresh water slips through the porous limestone terrain.

“I’m often asked why nobody has come there, and I say, ‘Well, probably because you need to be a little nuts to go there,” said Ivan Sprajc, the survey’s lead archaeologist and a professor at a Slovenian research center, ZRC SAZU. “It’s not an easy job.”

The work has been revolutionized over the last decade by lidar, a technology that uses airborne lasers to pierce dense vegetation and reveal the ancient structures and human-altered landscapes beneath. But in the end, it still comes down to arduous treks.

“Sprajc is doing precisely the right thing; using lidar as a survey instrument but not interpreting the results without ground-truthing,” said Rosemary Joyce, an anthropologist at the University of California, Berkeley.

She said in an email that it was unlikely for any newly documented site to “materially change historical narratives,” but that such work could help researchers see “more variation in the ways that different Maya communities carried out life during the Classic period.”

And it remains “unusual to find such a large site that nobody knows about,” said Scott Hutson, an archaeologist at the University of Kentucky.

For decades archaeologists relied on the help of descendants of the Maya to identify and excavate the ancient sites familiar to them. But because this part of Campeche has for decades been a preserve, Dr. Hutson said, “there’s simply been no archaeologists walking through this area at all.”

Dr. Martin called the region an “empty zone” on archaeologists’ maps.

Dr. Sprajc, 67, said the expedition to Ocomtún took about a month and a half, “relatively short” compared with the usual two months or more. The journey was made during the dry season, which can be daunting — but less so than long treks in the rainy season.

Surrounded by wetlands, Ocomtún includes pyramids, plazas, elite residences and “strange” complexes of structures arranged almost in concentric circles, Dr. Sprajc said. “We don’t know anything about that from the rest of the Maya lowlands,” he said.

The largest documented structure in Ocomtún was a pyramid about 50 feet tall, which Dr. Sprajc said would have been a temple. It and some other structures stood on a large rectangular platform, raised about 30 feet from the ground and with sides more than 250 feet long.

“Just by the scale of it, the location of it, it must be a significant site,” said Charles Golden, an anthropologist at Brandeis University. He said excavations could help answer a host of questions about who lived there and their relationship to other Maya cities and settlements.

People appeared to have left Ocomtún around the same time they did other Maya cities, from about 800 to 1000 A.D., a decline that researchers attribute to factors like drought and political strife.

A hint to those conflicts may have been found at the site. While most of the structures were unadorned the team found, upside down in a stairway, a block with hieroglyphics that appears to have been from another Maya settlement.

Such monuments were sometimes “brought as spoils of warfare from other sites, and this is what apparently happened in this case,” Dr. Sprajc said.

Dr. Joyce said that the block’s imagery of conquest was normal, “so we may have evidence here of Ocomtún being part of the great wars that swirled around the major powers” of the Maya world.

The team also found some agricultural terraces, which archaeologists called a sign of the Maya’s widespread modifications to make the difficult environment more bountiful for humans. Using hydraulics, water conservation and capture, and landscape engineering like terraces, the Maya managed to live in “what seem today pretty inhospitable areas,” Dr. Martin said.

For modern groups passing through, water has to be lugged in by truck. Dr. Sprajc said that even after his team had carved about 37 miles of drivable trail to Ocomtún, it still took five to 10 hours to reach the site because the terrain was so difficult to traverse.

Such expeditions require huge expenditures, both for the field work and before anyone sets foot in a forest. Lidar scans alone can cost tens of thousands of dollars. Dr. Sprajc found funding not only from his own institution, but also four Slovenian companies and two American charities: the publisher Založba Rokus Klett, the rail service Adria kombi, the credit company Kreditna družba Ljubljana, the tourism company AL Ars Longa, the Ken & Julie Jones Charitable Foundation and the Milwaukee Audubon Society.

Other researchers may now seek the funding, permits and supplies needed to excavate Ocomtún, but Dr. Sprajc will not be among them. He said he was busy planning a new expedition, next March or April, bound for another part of the Yucatán where lidar imagery has turned up leads.

Fellow scientists, buoyed by the work at Ocomtún, are looking forward to what his team might find next.

“This shows in places like Campeche, which on the one hand are pretty close to places like Cancún and heavy tourist sites, there’s still these places that nobody’s really documented,” said Dr. Golden, the Brandeis anthropologist. “So that’s always exciting that these places still have secrets to yield.”