Pyramid Builders of Kahun

Who built the mud-brick pyramid of Sesostris II and why did they disappear?

The Twelfth Dynasty of Egypt started out so well, with a new area for agriculture being opened up in the Fayyum by an ingenious canal, and yet it collapsed in ruin and was followed by the shadowy Thirteenth Dynasty whose weakness invited invasion by the Hyksos.

Yet the glory of the Twelfth was illusory, shown nowhere better than in the pyramids built by its kings. They looked fine, with their facings of gleaming Tura limestone, but beneath the stone was mud brick - millions of bricks made of mud mixed with straw. And much of the economy was based on a large number of Semitic slaves - though no one knows where they came from: purchase? Prisoners of war? Immigrants later reduced to slavery?

An even greater mystery is where they all went to, for one day the workmen on the pyramids simply disappeared, leaving their tools and household goods behind them. Why would women abandon their pretty pebble necklaces - unless they had found something better?

There are different opinions of how this first period of occupation at Kahun drew to a close ... The quantity, range and type of articles of everyday use which were left behind in the houses may indeed suggest that the departure was sudden and unpremeditated.
Rosalie David, The Pyramid Builders of Ancient Egypt p. 199