Participium relativum is a construct found in many languages where the participle, instead of being in a relative clause, is thrown to the beginning of the sentence as part of a prepositional phrase. Consider The man, who was sitting on the terrace, admired the silver Moon vs Sitting on the terrace the man admired the silver Moon.
This kind of construct is found in both the Quenya and the Noldo-Sindarin lines of Eldarin languages.
In Quenya the examples we have are from the Middle Quenya period. In the Quenya Verbal System essay we are first given an example of an imperfect participle used as participium relativum:
ampanaina i·már a·tatallanes "While it was being built people marvelled at the house"1 (Parma Eldalamberon 22 p. 109)
Within the same essay we also see examples of perfect participles used in the same way:
már karnelya e·tulle "having built a house he came" and már akárielya e utúlie (untranslated, but presumably "having built a house he has come") (ibid.)
In the other line of languages we have our attested example in Early Noldorin:
manthil sóg odog "having eaten he drinks a lot", and
manthil sóg odog en maint os eneg bhair “*having eaten he drinks a lot then he ate around six houses”
(Parma Eldalamberon 13 p. 128)
Although the attested examples are relatively (or, in the case of EN, quite) early, there is no reason not to assume that this kind of stucture was also found in the more mature versions of Quenya and Sindarin.
- 1. I think "a tatallanes" marks a medial voice: "they admired it"