Learn Farsi: بعضی از کارگرها مقبره را حفاری کرده بودند. - Some of the workers had excavated the tomb.

The verb is the compound حفاری کردن (to excavate). To make the past perfect, we use the past participle of the verb, which is حفاری کرده (excavated), and add the simple past of the helper verb 'to be' matching the subject 'they' (the workers), which is بودند. Together, this makes حفاری کرده بودند.

Why do we need the word را after مقبره (tomb)?

را points out the specific direct object of the sentence. Since the workers had excavated a specific tomb ('the tomb' rather than 'a tomb'), we must put را directly after مقبره.

How do you say 'some of' in Farsi, and does the noun after it need to be plural?

'Some of' is بعضی از. When referring to countable people or things, the noun after it should be plural. Here, the standard plural suffix ها is added to کارگر (worker) to make کارگرها (workers).

Why is the whole verb phrase pushed to the very end?

Farsi is a Subject-Object-Verb language. The subject block بعضی از کارگرها (Some of the workers) comes first, followed by the object block مقبره را (the tomb). Finally, the entire three-word compound verb حفاری کرده بودند sits at the very end.