A tiny, hand-painted sign mounted on a flimsy barbed wire fence warns visitors to Peru’s Nazca lines: “No entry. Area off-limits.” It’s not much of a deterrent. The latest threat to the vast U.N. World Heritage site, where enigmatic shapes and lines, stylized figures of birds and animals were etched in the desert 2,000 years ago, is a camp of around 30 shacks that appeared in August.

The rudimentary straw-matting huts are pitched in the dry earth on the fringe of a protected area that covers 111,200 acres (45,000 hectares) — roughly 2 1/2 times the size of Washington, D.C. Directly below them is an ancient burial site still pitted by long-ago scars of tomb raiders hunting for priceless textiles, pottery or jewels.

The lines — one of Peru’s top tourist attractions and properly visible only from the air — were made by clearing away surface shale or piling it up onto other stones when the Roman Empire still existed. But there are signs modern vandals have been at work.

One giant trapezoid, which is not on the usual tourist aerial overview, has graffiti scrawled all over it.

Nearby, someone has also drawn a penis — a recent addition, judging by how the newly disturbed earth stands out brightly against the gray of the plain.

“Everyone thinks we’re exaggerating when we say the lines are being irreparably damaged, but I’d like them to see the amount of graffiti on these lines,” said Eduardo Herran, chief pilot at Aerocondor, who flies over Nazca almost daily.