In 1915, a group of Russian engineers set out to build this particularly unusual armored fighting vehicle. At 40 tons, it was the largest tank in the worl at the time and had a ten-man crew.
Here's a drawing:
And here's a photo of a model:
The entire thing was designed as a gigantic tricycle. The large front wheels were about 30 feet in diameter and were each driven by a separate 240hp engine. The idea was that the large wheels would carry the vehicle over any obstacles encountered on the battlefield.
Here's a photo of the prototype on the testing grounds:
The main problem: while the large front wheels would've done a fine job of carrying this thing over battlefield obstacles, the weight on the tiny rear wheel was so great that it would constantly sink into any mud, sand, or even slightly soft ground. After a few miserably failed demonstrations, the Russian high commission decided that it was underpowered and (because it presented such a large target) vulnerable to artillery fire.
The prototype remained in the same spot where it had failed it's operational tests until 1923 when it was dismantled for scrap.