A defining (embedded) relative clause cannot typically be fronted (as Theme), since it functions as the Qualifier in a nominal group realising a direct or indirect participant.
A non-defining (ranking) relative clause can be fronted (in the clause nexus), as in:
Founded in 1690 by Prince Constantine Brancoveanu, the monastery of Horezu is a masterpiece of the ‘Brancovenesti’ style.*
Built by King Philip, the Royal Monastery of San Lorenzo El Real is a must-see of Madrid.°
See the discussion of these fronted non-finite hypotactic elaborating attributive clauses in Halliday & Matthiessen (2004: 404).
* analysis requested by Claudia Stoian on Sysfling, April 2012 (see here)
° analysis requested by Claudia Stoian on Sysfling, October 2012