A vardo's design includes large wheels set outside the body, whose sides slope outward considerably as they rise toward the eaves. Beyond this characteristic, the six types of caravans differ in shape, size, placement of the wheels relative to the bed, where made, and maker. The roofs of the bow-top and open-lot types are canvas stretched over curved wooden frames; the others are roofed in wood. By the mid-1800s, the designs were almost entirely standardized, and some features are common to all types. The door is almost always in the front.