Said to be celebrated (8)
I believe the answer is:
observed
This clue is a double definition.
'said' is the first definition.
(observing is a kind of saying)
'be celebrated' is the second definition.
(I've seen this before)
'to' acts as a link.
(Other definitions for observed that I've seen before include "Watched - obeyed" , "celebrated" , "Noticed or abided by" , "Abided by, rules say" , "Ascertained by sight" .)