Deus tuorum militum (RV612) is a Vesper hymn appropriate to the 'Common of One Martyr', what this means is that it could be sung as part of the liturgy on a feast day for a saint or martyr. I don't know who he composed it for but I'm pretty sure that it wasn't composed for the Pietà because as well as the normal strings it uses obbligato oboes – a practice not followed by the Pietà. I'd date it to some time during the 1720s and the setting as was normal for the time is alternatim that is he set only verses 1, 3, and 5 of the hymn leaving the even-numbered verses for performance either as plainsong for paraphrasing on the organ. The soloists in the live performance below were David Weygand (tenor) and Lyndon England, (countertenor). Enjoy :-).