One of the reasons Colditz was suitable to be refitted as a POW camp was that it was built on an outcropping of solid rock, making tunneling almost impossible. After serving as a general POW camp in 1939, it was later converted into a high security camp for recidivist escapees, the only amp in which guards outnumbered prisoners, the majority of the which were initially British, French, Poles, and Dutch. All in all, 130 prisoners escaped the grounds but depending on the source referenced, only 30, 31, or 32 of these were ultimately "home runs."