The Pattern controls Amber, and thus all Shadow that Chaos has not taken. Only because of The Patterns existence has Chaos been kept at bay at all. – Roger Zelazny’s Visual Guide to Castle Amber
The Pattern allows those descended from Dworkin to move through and control Shadow. It is known to have complete reflections in Tir-Na Nog’th and Rebma, and broken reflections throughout Shadow.
You can teleport to any place of your desire from the center of The Pattern, and it is considered a true coming of age for a Prince or Princess of Amber to walk The Pattern.
The Primal Pattern is the “true” Pattern, originally drawn by King Isidor. Even Amber itself is the first shadow of this Pattern.