1. Vihuela: A guitar-like instrument from Spain that was popular during the 16th century. It had a similar shape to the modern guitar and was played with a pick.
2. Quinterna: A five-stringed instrument that was popular in medieval Europe. It had a pear-shaped body and was played with a quill or plectrum.
3. Gittern: A small, guitar-like instrument that was popular in medieval Europe. It had a round body and was played with a quill or plectrum.
4. Lute: A guitar-like instrument that was popular in Europe during the Renaissance and Baroque periods. It had a pear-shaped body and was played with a quill or plectrum.
The modern guitar began to take shape in the 16th century when luthiers in Spain began to experiment with adding a sixth string to the vihuela. This new instrument, known as the guitar, quickly became popular throughout Europe and eventually became the most widely played stringed instrument in the world.
However, it is important to note that the evolution of the guitar did not strictly involve the modification of a single instrument. Different features and design elements were adopted from various instruments, resulting in the creation of the guitar as we know it today.