What is "built on"

Usage examples of "built on".

The town's small church, built on low stone walls similar to those that would give the convent the air of permanence it needed, was framed from foyer to auditori­.

In the raised hut the pirates had built on a sandy rise just inland of the fires, Beth Hurwood peered out at the sky and the sea, and filled her lungs with the cool sea air, and prayed that the breeze would hold until dawn.

But at various times, judging by the differences in workmanship between one section and another, the original structure seemed to have been built onto at random, apparently as the owner needed more space, and with little regard as to what had been built on before.