DEST began purchasing land at St Georgen/Gusen in May 1938. During 1938 and 1939, inmates of the nearby Mauthausen makeshift camp marched daily to the granite quarries at St Georgen/Gusen, which were more productive and more important for DEST than the Wienergraben Quarry. After Germany invaded Poland in September 1939, the as-yet unfinished Mauthausen camp was already overcrowded with prisoners. The numbers of inmates rose from 1,080 in late 1938 to over 3,000 a year later. At about that time, the construction of a new camp "for the Poles" began in Gusen about away. The new camp (later named Gusen I) became operational in May 1940. The first inmates were put in the first two huts (No. 7 and 8) on 17 April 1940, while the first transport of prisoners – mostly from the camps in Dachau and Sachsenhausen – arrived just over a month later, on 25 May.