The Origin of Yizkor

As I was reading the prayer for my relatives (Mother, Father, Siser, Grandmother.& Grandfather)who have passed on, I noticed this explanation of when the Yizkor prayer was first written and recited.

It was after the First Crusade 1099 when thousands of Jews were slaughtered.

Here is the Wikipedia link if you would like to read further.

http://en.wikipedia.org/wiki/Persecution_of_Jews_in_the_First_Crusade