Irregular verbs in English (to begin): Where they "had" begun - begun is the past participle of the verb "to begin" and requires the verb "to have" as a helper. Where they began - began is the simple past tense of the verb "to begin" and requires no helper verb. So in answer to your question, these can all be used in the sentence: Where they began OR Where they had begun, Where each began OR Where each had begun

The sentence has many mistakes - is it by a native speaker?? Where is it from? eg: began, not begun / around the mark, not marks / the following, not 'for'