Who built the concentration camps during the holocaust?

Answer 1

Except for the very earliest camps, the Nazi concentration camps were built on the orders of the SS. The actual building work was done by the first batch of prisoners, though in some cases existing, disused buildings were also used.

Answer 2

Most of the camp was built by inmates. The crematoria were supplied by J. A. Topf und Soehne, of Erfurt.

Answer 3

Actual construction was mainly done by the prisoners themselves, supervised by the SS.