At last, they came to the end. The strip ran to the foot of an ancient stone wall about fifteen feet high. The V-shaped ditch led to an opening in the bottom of the wall, where there was a hole about ten inches wide. They walked around the circular wall and saw that each of the other five strips met the wall in the same way, bringing the water in through small openings at its foot. They found that the wall was not a circle with a gap in it for a door or gate. It was a spiral, so that the circular wall stretched for a full three hundred sixty degrees, and then continued ten degrees past the beginning spot so it overlapped for about ten feet to form a narrow, curved corridor ending in an entrance. Sam and Remi sidestepped along the corridor and found themselves inside the circular wall. In the center was a pool of water.

They stepped to the edge and looked down. The pool was quite clear, about thirty feet deep. The bottom received no direct sunlight, at least not after the sun was low. The high stone enclosure around the pool included a walkway near the top that could be reached by a flight of steps.

“Why do you suppose they built a wall?” asked Remi.

“I don’t know,” said Sam. “Maybe during the last days of the city they needed to protect their water. Maybe it was the last line of defense if the city was taken. You could do worse than control the water supply in a siege. And, look, this place is only about thirty feet wide. It would be easy to defend. The walls are about six feet thick at the bottom.” He walked along the wall and picked up a loose rock, then looked across the enclosure. “This rock seems to be a plug. The other holes have fitted stones blocking them too. That would protect the water from poison.”

“I think its time to let Selma and Dave know that we found it,” said Remi.

“You’re right,” said Sam. “Let’s take a few pictures and send them first thing so Dave can tell us what we’ve found.”

Remi took pictures of the well, the pool, the curved entryway, and then stood on the battlement and took pictures in every direction. She added them to the pictures she had taken from the pyramid and on the strip and sent them. Then she waited a minute and called Selma.

“Selma here. Fire away.”

“We’ve found it. We’re on the site, and I’ve just sent you some pictures. Tell Dave Caine that the map is right. There’s a pool of water here with a stone margin around it and a high wall above it. It’s clear, and it seems to be quite deep—thirty feet or more.”

“What are those flat areas I’m seeing? Roads?”