Here is a URL and a quote about pasch, paschal

http://www.st-matthew.on.ca/bulletin/tridex.htm



The earliest shape of the Triduum begins to emerge in the church around the 2nd century with the development of a 2 day
pasch, a "bi-duum": fasting all day Saturday, all night long vigil that night ending with the celebration of the Easter sacraments
Sunday morning at dawn. The celebration of the pasch reaches its heights during the 5th-6th centuries, with a three day event
being celebrated.