The trouble was old and bureaucratic, the kind that festers for generations. When Chile and Argentina submitted their irreconcilable border claims to British arbitration in 1902, a demarcator named Herbert Leland Crosthwait was sent to mark the line through this trackless country. South of Lake O'Higgins, short on time, he fixed boundary marker 62 with a pile of stones and a slip of paper sealed in a bottle. From there the line was meant to run to Mount Fitz Roy - but exactly how it ran through the Laguna del Desierto valley was never beyond dispute. Then in 1946, aerial reconnaissance flown for the Chilean government revealed that the lake drained not to the Pacific but eastward, toward the Atlantic. The maps had been wrong. The argument reopened.

By 1965 Argentina was a nation primed for conflict, though not over a Patagonian lake. President Arturo Illia governed a country seething with the unfinished business of Peronism, his administration mocked in the press as slow and weak - he was nicknamed the turtle - while sections of the military openly agitated for a coup. Against that backdrop, the two presidents had actually met at the end of October and agreed to calm the frontier: withdraw forces, build nothing further. Yet within days, Argentine commanders launched an operation at Laguna del Desierto anyway, flying gendarmerie squadrons into the zone aboard DC-3 transports, trailed by magazine journalists and photographers. Whatever had been agreed in the capitals, the men on the ground were moving toward a confrontation.

The Chilean patrol was small and ordinary: Major Miguel Torres, Lieutenant Hernan Merino Correa, Sergeant Miguel Manriquez, Lance-Corporal Victor Meza, and two carabineros, Julio Soto and Jose Villagran. They were policemen, not soldiers of an invading army, sent to a shelter south of the lake. At two in the afternoon on 6 November, Major Torres received orders to return to the station. Two of the men went to fetch the horses; the others readied to leave. At twenty to five, roughly 90 Argentine gendarmes surrounded them. The Chileans, seeing the encirclement, called out to talk. Instead, gunfire cut them down. Merino was killed where he stood. Manriquez was wounded. The survivors were captured and taken, with the lieutenant's body, to an army barracks at Rio Gallegos.

Three days later the captured men were released and flown home with an envoy of President Eduardo Frei Montalva. Chile's foreign minister, Gabriel Valdes, condemned the killing as an unprecedented and inexcusable act in the history of the two countries' boundary disputes. For Chile, Hernan Merino Correa became something larger than a fallen policeman. His body was carried to Santiago for a state funeral and interred beneath the monument to the glories of the Carabineros. The frontier academy of the Carabineros was named for him, and so were streets and schools across the country. He came to embody an ideal - the officer who gives everything, even his life, for the homeland. He was a young man doing his duty in a place at the literal edge of his nation, and a single bullet made him a national symbol of sacrifice.

The killing rippled outward. The Argentine general who had planned the Laguna operation, Julio Alsogaray, would help lead the coup that toppled President Illia in June 1966, walking into the president's office before dawn to invite him to resign. The border question itself dragged on for another generation. Only in 1994 did an international tribunal finally rule on the valley, awarding almost all of it to Argentina; after a rejected appeal, Chile accepted the verdict in 1995. The two governments never agreed on what happened that afternoon - each blamed the other for firing first, and Argentina never held an official inquiry. What is not in dispute is the result: a contested patch of forest and water that cost a young man his life and left a scar on two nations that took thirty years to close.