Sentence Correction

Many of the earliest known images of Hindu deities in India date from the time of the Kushan Empire, fashioned either from the spotted sandstone of Mathura or Gandharan grey schist.

I am facing issues in identifying whether a particular term is a participle or a verb for eg" fashioned " as mentioned in the above question.
1. Why is fashioned a participle and not a verb?

secondly,

As per the explanation given states the verbs date and fashion should be in parellel. Why is so kindly guide.

Many of the earliest known images of Hindu deities
in India date from the time of the Kushan Empire,
fashioned either from the spotted sandstone of
Mathura or Gandharan grey schist.
(A) Empire, fashioned either from the spotted
sandstone of Mathura or
(B) Empire, fashioned from either the spotted
sandstone of Mathura or from
(C) Empire, either fashioned from the spotted
sandstone of Mathura or
(D) Empire and either fashioned from the spotted
sandstone of Mathura or from
(E) Empire and were fashioned either from the
spotted sandstone of Mathura or from

In the idiom either X or Y, EITHER and OR are known as SEESAW conjunctions.
The reason is that -- like two people on a seesaw -- X and Y must BALANCE EACH OTHER.

(A) either from the spotted sandstone of Mathura or Ganharan grey schist.
(B) either the spotted sandstone of Mathura or from Gandharan grey schist.
(C) either fashioned from the spotted sandstone of Mathura or Gandharan grey schist.
(D) either fashioned from the spotted sandstone of Mathura or from Gandharan grey schist.
(E) either FROM THE SPOTTED SANDSTONE OF MATHURA or FROM GANDHARAN GREY SCHIST.

Only E offers the required parallelism.

The correct answer is E.

Why is fashioned a participle and not a verb?

The images fashioned from sandstone.
Here, fashioned from sandstone is an ADJECTIVE serving to describe the images.
What KIND of images?
Images FASHIONED FROM SANDSTONE.

To serve as a VERB, fashioned must be preceded by a helping verb such as were, are, have been:
The images WERE FASHIONED from sandstone.
The images ARE FASHIONED from sandstone.
The images HAVE BEEN FASHIONED from sandstone.