Learn Hardcore German: Das alte Bürogebäude brannte vor vielen Jahren vollständig ab. - The old office building burned down completely many years ago.

In German every noun has a fixed gender. The word Gebäude (building) is grammatically neuter, so its definite article in the nominative case is das. When you form a compound noun like Bürogebäude (“office building”), it keeps the gender of its last element, Gebäude, hence das Bürogebäude.

Why is the adjective alte not altes or alten?

Because the noun is preceded by the definite article das, German uses the weak adjective inflection. In the nominative neuter singular, the weak ending is -e, giving das alte Bürogebäude. If there were no article, you’d use the strong ending -es (e.g. altes Bürogebäude).

Why is the verb abrennen split into brannte … ab, with ab at the end?

abrennen is a separable-prefix verb. In main clauses the prefix ab detaches and moves to the end of the sentence. The stem verb then conjugates normally:
– Infinitive: abrennen
– Präteritum: brannte + ab → brannte … ab

What is the rule for placing vor vielen Jahren, vollständig, and the separated prefix ab in this sentence?

German generally orders adverbials as Time → Manner → Place, then the separable prefix. Here you have:

vor vielen Jahren (time)
vollständig (manner)
ab (separable prefix)
So: brannte (verb) + vor vielen Jahren
- vollständig
  - ab.

Why is vor vielen Jahren in the dative plural, and why does Jahren take -n?

The preposition vor (when meaning “ago”) always takes the dative case. In the dative plural most nouns add an -n if they don’t already end in -n. Thus viele Jahre (many years) becomes vielen Jahren after vor.

Why is this sentence in the simple past (Präteritum) rather than the present perfect (Perfekt)?

In written narratives, reports or historical accounts German prefers the Präteritum (“brannte ab”). In everyday spoken German you’d more often hear the Perfekt: „Das alte Bürogebäude ist vor vielen Jahren vollständig abgebrannt.“ Both are correct; Präteritum feels more formal or literary.

What does vollständig mean here, and is it acting like an adverb?

vollständig translates as “completely” or “entirely.” Although it’s technically an adjective, here it modifies the verb abrennen, so it functions adverbially (answering “How?” the building burned down).

Are there alternative ways to say “many years ago” in German?

Yes. Common equivalents include:

vor langer Zeit (“a long time ago”)
vor etlichen Jahren (“quite a few years ago”)
einst (poetic, “once/upon a time”)
Each carries a slightly different nuance, but they all indicate a past time frame.