When was the guitar invented, huh i was thinking about this question for several days and found that guitar was invented during 16th century somewhere in Spain, by the people called malaga. During that time the guitar used to have 4 strings tuned in  C F A D, the similar concept we have now in the miniature form of Ukulele. During 17th and 18th century guitar went through many design changes and allowed the addition of 5th and 6th string to it. In India, there are some instruments like veena, sitar etc. which were in place before the birth of guitar, these instruments were played by greatest players of era entertaining kings, queens and the mass crowd during that time.