Petrus de Cruce (also Pierre de la Croix) was active as a cleric, composer and music theorist in the late part of the 13th century. His main contribution was to the notational system.
HistoryLayer draws the world as it was in any year from 123,000 BCE to
2026. Move the slider and the borders redraw for that year; the map
carries 23,890 events, 12,790 people, 837 wars and 13,183 cities, each
one readable in place. Signing in is optional and lets you keep what
you find.