Marco Polo (1254-1324) was an Italian voyager and merchant who was one of the first Europeans to travel across Asia through China, visiting the Kublai Khan in Beijing. He left in 1271 (he was a teenager at the time) with his father (Nicolo Polo) and uncle (Maffeo Polo); they spent about 24 years traveling.
The pitch of each consecutive fret is defined at a half-step interval on the chromatic scale. Standard classical guitars have 19 frets and electric guitars between 21 and 24 frets, although guitars have been made with as many as 27 frets. Frets are laid out to accomplish an equal tempered division of the octave.