Who invented a system of writing down music down?

The system of writing down music, known as musical notation, has evolved over centuries. The earliest forms can be traced back to ancient Greece, but significant developments occurred in the 9th century with the introduction of neumes by the Catholic Church to notate Gregorian chant. The modern staff notation we use today was developed in the late Middle Ages, with Guido of Arezzo being a pivotal figure in its evolution.