Cum calor magnus esset, nos sub umbra arborum sedebamus et aquam bibebamus.

Esset is the imperfect subjunctive of sum. After cum, Latin very often uses the subjunctive when the clause gives circumstance, cause, or concession in a past narrative. So cum calor magnus esset is not just a bare time marker; it presents the heat as the background condition.

If Latin had cum calor magnus erat, that would sound more like a straightforward factual when the heat was great. With esset, the clause feels more like narrative background.

It is imperfect because it describes an ongoing state in past time. The heat was not a one-moment event; it was a continuing condition while the other actions were happening.

That matches the main verbs sedebamus and bibebamus, which are also imperfect and describe ongoing past actions.

Both are imperfect indicative, first person plural. The imperfect usually describes:

• an ongoing action in the past: we were sitting, we were drinking
• or sometimes a repeated/habitual action: we used to sit, we used to drink

In this sentence, they most naturally describe a scene in progress: we were sitting under the shade of the trees and drinking water.

Yes. The endings of sedebamus and bibebamus already tell you the subject is we, so nos is not grammatically necessary.

When Latin includes nos anyway, it is usually for emphasis, contrast, or clarity. So nos can suggest something like we, for our part or simply put a little more stress on the subject.

Latin does not have articles like English the and a/an. That means calor magnus can mean the great heat, a great heat, or simply great heat, depending on context.

The same is true for aquam: it can be water, the water, or some water, depending on what the sentence is talking about.

They belong together because magnus is an adjective agreeing with calor in:

• gender: masculine
• number: singular
• case: nominative

So calor magnus means great heat or the heat was great. Even if the word order changed, the matching endings would still show that magnus describes calor.

Calor is nominative singular because it is the subject of esset. In other words, the heat is what was great.

The adjective magnus is also nominative singular masculine to match it.

Umbra is ablative singular here, used after sub. With sub, Latin commonly uses:

• ablative for location/rest: under
• accusative for motion toward: to a position under

So sub umbra means under the shade, with the idea of staying there, not moving there.

Arborum means of the trees. It is genitive plural because it depends on umbra: the shade of the trees.

So the phrase breaks down like this:

• sub = under
• umbra = shade
• arborum = of the trees

Together: under the shade of the trees.

Latin is thinking of one area of shade produced by several trees. That is perfectly natural. English can do something similar too: the shade of the trees.

So the singular umbra does not mean there was only one tree; it means there was one shaded area or one mass of shade.

Aquam is the direct object of bibebamus. It answers the question what were we drinking? The answer is water.

That is why it appears in the accusative singular.

Latin word order is much more flexible than English word order because the endings show the grammatical relationships. Verbs often come near the end, especially in more literary or formal Latin, but they do not have to.

So sedebamus and bibebamus are late in the sentence because that is a very normal Latin way to arrange the words, not because the meaning changes.

Yes. The two imperfect verbs joined by et present two actions as part of the same ongoing scene. The sentence paints a picture: we were sitting and drinking water while the heat was great.

So the effect is not two sharply separated events, but one continuous situation.

Yes. Cum calor magnus esset, sub umbra arborum sedebamus et aquam bibebamus would still be completely correct Latin.

Including nos just adds emphasis. That is a common feature of Latin: subject pronouns are often omitted unless the writer wants to highlight them.