In ten more minutes, they reached the head of the path. They climbed up onto the level top of the plateau and looked around. There were several large mounds of earth that might be buildings, but they were not on the scale of the buildings in the cities they had found. They weren’t high or steep, and the plateau wasn’t large enough for monumental architecture. It was only about three hundred feet across.

They both noticed something else. The perimeter of the plateau had a low ridge around it like the rim of a bowl. They walked along the ridge, taking pictures, and then Sam stopped at a section that had fallen down. It revealed the ridge to actually be a pile of stones and earth.

“It’s a wall. It’s like the old Roman forts you find in Europe—low walls of stone piled up to stop an enemy attack. This was built for a battle.”

“It’s not like any of the other ruins we visited,” Remi said. “It feels different—not empty, somehow.”

They walked the rest of the way around the plateau. In the middle of the flat space, there were more low mounds of earth and stone, all of them overgrown with small plants. The only sounds on the plateau were the movements of the leaves in a soft wind and the calls of birds. At times, it was so quiet that Sam’s and Remi’s footsteps were the loudest sounds.

Remi said, “This isn’t a place where people would live. It reminds me of the cenote a few miles from here. The wall around it seemed to be made for a last stand too.”

“I know what you mean,” said Sam. “This and the cenote must be relics of a war between cities.”

They came across a trench about three feet deep and only wide enough for a man to stand in it and dig. It ran from the stone wall at the rim of the plateau for about a hundred feet and directly into one of the mounds. “Uh-oh,” said Remi.

“Do you know what that is?”

“I think it’s the kind of trench that pot hunters and grave robbers dig to find underground chambers and caches.”

Sam raised his satellite phone and took a few pictures of it, then sent them to Selma. He and Remi walked along the trench, looking into it. “If that’s what it was, it seems to have failed. It doesn’t lead to a bigger hole, where they might have found something and dug it up.”

The trench stopped at the base of the mound. When they reached the spot, Remi said, “It doesn’t seem to have stopped here. The rocks that are piled on the side of the mound are different. I think somebody dug into the mound and then covered the hole after they were done.”

“It’s puzzling,” said Sam.

“The word is ‘creepy,’” Remi said.