To-verb: This is the short form of 'in order to' and is used to convey an intent or purpose. For example,
I practiced for nine hours every day to make my moves perfect. <correct>
What was my purpose? To make my moves perfect.
Note that the presence of a comma before 'to' is unnecessary and therefore, incorrect.

Verb-ing: This is used when no intent/purpose is to be conveyed.

In your question, the objective/purpose behind the use of animal-hide shields is not relevant. Therefore, the use of 'to protect' is incorrect.

Gowri@CrackVerbal wrote:To-verb: This is the short form of 'in order to' and is used to convey an intent or purpose. For example,
I practiced for nine hours every day to make my moves perfect. <correct>
What was my purpose? To make my moves perfect.
Note that the presence of a comma before 'to' is unnecessary and therefore, incorrect.

Verb-ing: This is used when no intent/purpose is to be conveyed.

In your question, the objective/purpose behind the use of animal-hide shields is not relevant. Therefore, the use of 'to protect' is incorrect.

Hi Gowri,
Thanks for the reply!
But what do you mean by saying "In your question, the objective/purpose behind the use of animal-hide shields is not relevant."? Please explain.
Also, I "think" , protecting should be derived from , which are protecting while the which points shields. If that is so, then why can't the same concept be applied to "to protect?"

Let's simplify the sentence and look at option E.
Animal-hide shields were essential military items, to protect warriors.
This is incorrect.

You cannot use an infinitive after the comma unless the sentence were to be rewritten this way:

Animal-hide shields were essential military items, designed to protect warriors.
Animal-hide shields were essential military items, made to protect warriors.