The history of denim is inextricably linked to the history of cotton. As of the 12th Century cotton became widespread in Europe and was preferred to linen due to its strength and colourfulness.
At this point moleskin becomes available which is denim’s predecessor and as a fabric shares some of the same characteristics. The main European, moleskin-producing cities were Nimes and Genoa and it is in these places where Denim (literally, of Nimes) and Jeans (of Genoa) originate as fabrics.
The defining characteristics of the fabrics as of the mid-1800s are the colour of the warp (vertical) and the weft (horizontal) yarns used in weaving. In denim the warp is blue and the weft white, while in jeans warp and weft yarns are both the same colour; almost always blue. After the 1800s, the tow words become almost synonymous indicating both the fabric and the garment.