Every year, almost all the inhabitants gather at the memorial and celebrate this anniversary.

memorial 是名词，由动词 memorize（记忆）的词根 memor-（记忆）加上后缀 -ial（与...有关的）构成，意思是"纪念物、纪念碑"，指为纪念某人或某事而建立的建筑物或场所。