For camouflage they were often built near farms. Elements Standard construction elements such as large Regelbau bunkers, smaller concrete "pillboxes", and "dragon's teeth" anti-tank obstacles were built as part of each construction phase, sometimes by the thousands. Frequently vertical steel rods would be interspersed between the teeth. This standardisation was the most effective use of scarce raw materials, transport and workers, but proved an ineffective tank barrier as US bulldozers simply pushed dirt bridges over these devices. "Dragon's teeth" tank traps were also known as Höcker in German ('humps' or 'pimples' in English) because of their shape. These blocks of reinforced concrete stand in several rows on a single foundation. There are two typical sorts of barrier: Type 1938 with four rows of teeth getting higher toward the back, and Type 1939 with five rows of such teeth. Many other irregular lines of teeth were also built. Another design of tank obstacle, known as the Czech hedgehog, was made by welding together several bars of steel in such a way that any tank rolling over it would get stuck and possibly damaged. If the contour of the land allowed it, water-filled ditches were dug instead of tank traps. Examples of this kind of defence are those north of Aachen near Geilenkirchen. Working conditions The early fortifications were mostly built by private firms, but the private sector was unable to provide the number of workers needed for the programmes that followed; this gap was filled by the Todt Organisation. With this organisation's help, huge numbers of forced labourers – up to 500,000 at a time – worked on the Siegfried Line. Transport of materials and workers from all across Germany was managed by the Deutsche Reichsbahn railway company, which took advantage of the well-developed strategic railway lines built on Germany's western border in World War I. Working conditions were highly dangerous. For example, the most primitive means had to be used to handle and assemble extremely heavy armour plating, weighing up to . Life on the building site and after work was monotonous, and many people gave up and left. Most workers received the West Wall Medal for their service. In propaganda German propaganda, both at home and abroad, repeatedly portrayed the Westwall during its construction as an unbreachable bulwark. At the start of the war, the opposing troops remained behind their own defence lines. As a morale booster for British