At Auschwitz, the corpses were incinerated in crematoria and the ashes either buried, scattered, or dumped in the river. At Sobibór, Treblinka, Bełżec, and Chełmno, the corpses were incinerated on pyres. The efficiency of industrialised killing at Auschwitz-Birkenau led to the construction of three buildings with crematoria designed by specialists from the firm J.A. Topf & Söhne. They burned bodies 24 hours a day, and yet the death rate was at times so high that corpses also needed to be burned in open-air pits.