The preposition در (“dar”) marks the locative case in Persian. The locative is a grammatical case that typically indicates place. In Persian, it is also used to indicate time and consequently, it can be viewed as a case that marks a location in place or time. In Latin, the ablative and the accusative cases are used to specify time. Persian makes a clear distinction and uses the ablative for “motion from” (i.e. source), the dative for “motion to” (i.e. target) and the locative for the exact location.

به تهران می‌روم
Be Tehrân miravam
I go to Tehran
از تهران می‌آیم
Az Tehrân miâyam
I come from Tehran
در تهران زندگی می‌کنم
Dar Tehrân zendegi mikonam
I live in Tehran

Marking the locative case in Persian is similar to languages like Turkish and Japanese in that a single adposition or particle is used to indicate time or place rather than an inflected form. This is different from languages like English that lack a unique word to indicate place or time.

در خانه
dar xâne
at home
در تلویزیون
dar televizyon
on TV
در سال ۱۹۹۴
dar sâl-e 1994
in 1994
در ماه سپتامبر
dar mâh-e septâmbr
in September
در آن روز
dar ân ruz
on that day
در آن زمان
dar ân zamân
at that time
در ساعت هفت
dar sâat-e haft
at seven o’clock
در عرض چند ساعت
dar arz-e čand sâat
within a few hours