Learn Farsi: اگر قمقمه را نداشتیم، روی این تپه می‌مردیم. - If we did not have the canteen, we would die on this hill.

This sentence is an "unreal" or hypothetical conditional—they actually do have the canteen. In Farsi, when you talk about a present condition that isn't true, the اگر (if) clause uses the simple past tense. The subjunctive is generally reserved for "real" or possible conditions.

Why is the past continuous verb می‌مردیم used here to mean "would die"?

In the result clause of an unreal conditional sentence, Farsi uses the past continuous tense (the prefix می‌ + past stem + personal ending) to express what would happen. Even though it looks like "we were dying," in an اگر (if) sentence, it translates to "we would die."

What is the infinitive of می‌مردیم and how is the word built?

The infinitive is مردن (mordan), meaning "to die," and its past stem is مرد (mord). To build this conjugated form, you combine the continuous prefix می‌ (mi), the past stem مرد, and the first-person plural ending ـیم (-im).

Why is the object marker را used after قمقمه (canteen)?

را (rā) is required because it marks a specific, definite direct object. The speakers aren't talking about hypothetically lacking any canteen; they are talking about the specific canteen they are currently carrying.