This post is really a precis of a terrific article in Gramophone (June 2012) by William Yeoman. My take on this is that when you find a beautifully concise and elegant little article on the how the classical guitar has evolved from the 16th-Century Spanish courts, up to today, go with it!
In the C16, the two instruments in common use were the four-course (a course is a double string arrangement, rather than a single string) Renaissance guitar and the lute (image far left).
The guitar of the 17C became physically larger and more ornate in decoration, as well as a fifth-course being added (image No. 3). During this Baroque period, the technique of playing generally improved including the use of strumming (rasgueado) and plucking the strings (punteado). This was also the century of Gaspar Sanz (see a previous post about his music) and the period rings with dances entitled Preludes, Allemandes, Sarabandes, Chaconnes and other lovely French words! The Baroque guitar had a lovely characteristic effect, known as campanelas (little bells) whereby notes were allowed to over-ring during fast pages of music. It’s a wonderful sound specific to the instrument in this period.
By the time we get to the late C18 and early-C19, the guitar gained its sixth string and the recognizable figure-of-eight shape. (image No. 4). At this point we gain the composers and players including Fernando Sor, Dionysio Aguado, Mauro Giuliani amongst others whose pieces are well-known to all contemporary classical guitarists.
The Romantic period in music (mid-to-late-C19) gave us some great guitar makers, one of the most famous being Antonio de Torres Jurado (1817-92). The Torres is, essentially, today’s classical guitar (image No. 5). It is defined by its larger body and the fan bracing technique (the struts supporting the soundboard top-piece of the guitar). Today, expert luthiers have spent much time looking at different types of bracing systems, as well as using different timbers and other more radical innovations too technical to go into here.
And there you have it, a quick travelogue of guitar development over four centuries.