The playing of conventional chords is simplified by open tunings, which are especially popular in folk, blues guitar and non-Spanish classical guitar (such as English and Russian guitar). For example, the typical twelve-bar blues uses only three chords, each of which can be played (in every open tuning) by fretting six-strings with one finger. Open tunings are used especially for steel guitar and slide guitar. Open tunings allow one-finger chords to be played with greater consonance than do other tunings, which use equal temperament, at the cost of increasing the dissonance in other chords.
Guitars have been played since the Renaissance era, after descending from the ancient Greek instrument, the kithara. Or, at least, that's how the theory goes: the only real proof for this is the similarities between the Greek word and the Spanish word, quitarra. Early guitars often had four strings, evolving into the six-string version we know today in the late 1600s. Anton Stradivari, the famous violin-maker, also had a hand in making guitars. There's now only one Stradivarius guitar left in existence.