In order to say that something ‘was’ a certain way in Japanese, you will need to use
だった (casual) or
でした (polite) attached to the end of a noun or
な-Adjective. This is simply a combination of two auxiliary verbs,
だ (or
です when polite) with た. For
だった, we will need to add った to the base form of
だ. For
です, す will change to し before adding た.
-
あの電車（でんしゃ）は静（しず）かだった。
That train was quiet.
-
富士山（ふじさん）は綺麗（きれい）でした。
Mt. Fuji was beautiful.
The past form of い-Adjectives cannot be linked with だった or でした, as they have their own set of conjugation rules.