Streamlining with Passive Participles
While active participles describe what a noun is doing, passive participles describe what is being done to it. They let you condense complex который clauses into streamlined phrases, turning "the artifact which was found by archaeologists" into "the artifact found by archaeologists."
Just like active participles, passive participles are verbal adjectives. They decline to match their noun in gender, number, and case. When a participle phrase immediately follows the noun it describes, it is set off by commas.
Past Passive Participles (-нный, -тый)
To describe a completed action, use the past passive participle. These are formed from perfective verbs and typically end in -тый or -нный (sometimes -ённый or -енный).
Expressing the "Doer" (The Agent)
In English, we use "by" to show who performed a passive action (e.g., "built by the architect"). In Russian, simply put the noun representing the doer into the instrumental case.
Present Passive Participles (-емый)
To describe an ongoing or regular action (like a blueprint currently being discussed or a monument regularly protected), use the present passive participle. These are formed from imperfective verbs and usually end in -емый.
Declining Passive Participles
Because they function as adjectives, passive participles must match the case of the noun they modify. If you are talking about the architecture of the ruins (genitive case), the participle modifying "ruins" must also be in the genitive case.