Ancient religion Amritsar and Zion so reformed (14)

I believe the answer is:

zoroastrianism

'ancient religion' is the definition.
(Zoroastrianism is a religion)

'amritsar and zion so reformed' is the wordplay.
'and' means one lot of letters go next to another.
'reformed' is an anagram indicator.
'amritsar'+'zion'+'so'='amritsarzionso'
'amritsarzionso' is an anagram of 'ZOROASTRIANISM'.

(Another definition for zoroastrianism that I've seen is " Ancient religion that originated in Persia".)

I've seen this clue in The Times.

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