(CNN)The graffiti, written in a French chalk quarry and dating back almost 100 years, is plain and stark. "HJ Leach. Merely a private. 13/7/16. SA Australia," reads one inscription. "HA Deanate, 148th Aero Squadron, USA. 150 Vermilyea Ave, New York City," another says. "9th Batt Australians, G. Fitzhenry, Paddington, Sydney, N.S.W., 1916 July; Alistair Ross, Lismore, July," reads a third. They were World War I soldiers, four of almost 2,000, whose writings have recently been found underneath battlefields near Naours, France, about 120 miles north of Paris. Photographer Jeff Gusky, who has been chronicling details of the site, describes the inscriptions -- and the underground city in which they were found -- as "breathtaking." "This is a treasure trove," he said Monday night from his home in East Texas, where he works as an ER doctor. "Even locally, no one realized what was there." Gusky, a National Geographic photographer, has chronicled the area in a portfolio he calls "The Hidden World of WWI." The revelations of the underground city, which extends for miles in some directions, have come to light recently only because of a series of events, Gusky said. The underground city actually dates back centuries but was sealed up in the 18th century. It was rediscovered in the late 19th century. During World War I, soldiers would take refuge in the carved-out rooms and pathways. The front was sometimes mere miles away; the Battle of the Somme, one of the bloodiest in world history, was fought nearby in 1916. The land was privately owned for many years and generally off-limits to outsiders, said Gusky, but it changed hands in 2013. The rights to operate it were purchased by a consortium of villages that wanted to promote awareness of the area's history, he said. Researching the city is a painstaking task. For one thing, it's dark, so observers generally haven't realized what's in there until they've gone exploring. Moreover, the maze-like extensiveness of the site has made discovery a slow process. "They go on and on and on. They're so elaborate in some places, there are maps carved into stone so the soldiers wouldn't get lost," he said. The graffiti looks like it was written yesterday, he added. Gusky has noted 1,821 names. About 40% are Australian, with most of the others identified as British. Fifty-five are Americans, and 662 have yet to be traced. For Gusky, the graffiti provides a human connection with men who lived a century ago. In many cases, they just wanted to be remembered, he said. "Someone could be in this place one day and the next fighting at the front," he said. Leach, "merely a private," was killed a month later in battle, Gusky observed. "It could very well have been the last time he recorded his name as a living, breathing human being," he said. 7 things you didn't know about the man who started WWI .
World War I graffiti is discovered in an underground quarry .
The writings are generally plain, with listings of names and places .
Photographer: Graffiti a human connection to the past .