The scholar and music theorist Isidore of Seville, while writing in the early 7th century, considered that "unless sounds are held by the memory of man, they perish, because they cannot be written down." By the middle of the 9th century, however, a form of neumatic notation began to develop in monasteries in Europe as a mnemonic device for Gregorian chant, using symbols known as neumes; the earliest surviving musical notation of this type is in the "Musica disciplina" of Aurelian of Réôme, from about 850. There are scattered survivals from the Iberian Peninsula before this time, of a type of notation known as Visigothic neumes, but its few surviving fragments have not yet been deciphered. The problem with this notation was that it only showed melodic contours and consequently the music could not be read by someone who did not know the music already.