Learn Hardcore Russian: Длинная река тянется через город. - The long river stretches across the city.

Because река is a feminine noun in the nominative singular, the adjective must agree with it in gender, number, and case. That’s why you see длинная (feminine, nominative, singular).

Why is река in the nominative case and not the accusative?

Река is the subject of the sentence (it’s what “stretches”), and since тянуться is an intransitive verb here, the subject appears in the nominative case.

What does the verb тянуться mean, and how is it different from тянуть?

Тянуться (imperfective, reflexive) means “to extend,” “to stretch out,” or “to pull itself,” whereas тянуть (imperfective, non-reflexive) means “to pull” something (you or another agent pulls a direct object).

What is the function of the -ся suffix in тянется?

The -ся suffix makes the verb reflexive or passive. In this sentence, it shows that the river “stretches out by itself,” i.e. it extends across the city without an external agent.

Why is город unchanged in через город? Isn’t that accusative?

The preposition через does require the accusative case. Город is an inanimate masculine noun whose nominative and accusative forms are identical. So you see город in both cases.

Which case does the preposition через govern, and why?

Через always governs the accusative case when you want to express movement “through” or “across” something. Here it shows the river moves across the city.

Why are there no articles like “a” or “the” before длинная река?

Russian doesn’t have definite or indefinite articles. Context alone tells you whether you mean “a long river” in general or “the long river” you have in mind.

What’s the difference between длинная and долгая?

Длинная refers to physical length or spatial extent (“long in space”), while долгая describes time or duration (“long in time”). You wouldn’t say долгая река, because you’re talking about its length, not its duration.