They were first used to plough fields and then used as armoured tanks in WWI, today, they are used to dig canals, raise tons of earth, move large boulders, carry chunks of coal and everything else related to earthmoving. The lowly bulldozer is can be found on very major construction site throughout the world, and one of the most popular and recognizable brand is the Caterpillar (mustard color). Here's a bulldozer papercraft model from paperboxworld, free download is available at the link below.
Bulldozer - [Download Page]