The operation, which started at 4 am, is seizing 44 items stored in the Catalan Museum of Lleida.
The items are originally from Sijena convent in Aragon, which claims they were sold illegally by its nuns.
The operation, ordered by Madrid, comes as tension over Catalan independence continues.
The legal dispute over the items dates back to the 1980s, when after moving their order to Barcelona, the nuns struck a deal with the Catalan government for the sale of the pieces, which include medieval sarcophagi, 16th century alabaster reliefs and 18th century paintings.
While Madrid has direct rule over Catalunya, Spain’s culture minister has signed a judicial order for the return of the treasures, with a midnight on Sunday deadline.
Challenges have been launched by local authorities and the museum, arguing that the case is still under appeal.
But the Guardia Civil have been authorised to seize them ‘with force if necessary’ – a move which museum director Josep Giralt said risks turning the operation into ‘a battlefield’.
The CUP, a hardline secessionist party, called on Catalans to ‘defend’ the artifacts as they had polling stations during the illegal October 1 referendum.
Mireia Boya, a CUP parliamentarian from Lleida, said the removal was aimed at ‘humiliating Catalunya’, and the case should be taken up ‘as a banner of resistance against (Article) 155’.
In 2015, after years of contradictory rulings and appeals, an Aragonese court found that the sales were illicit, and ordered the treasures returned. But Catalonia refused to comply, lodging an appeal which has yet to be ruled upon.
- British RAF pilot brings new – and MUCH cheaper – property listing concept to Spain - 23 Mar, 2019 @ 17:21
- Spain’s Supreme Court bans historic bull hunting and spearing tradition in Castilla y Leon - 23 Mar, 2019 @ 11:00
- Malaga’s ‘Banksy’ attracts world attention replicating masterpieces on the streets of Spain and Europe - 23 Mar, 2019 @ 10:00
- M1 Legal is stacking up the victories against Spain’s Timeshare giants - 22 Mar, 2019 @ 11:13
- How to Improve Academic Writing Skills for UK University Admission - 22 Mar, 2019 @ 09:37
- Giant electricity pylons rampaging across the valley vista in Sierra Nevada - 21 Mar, 2019 @ 18:57
- Living with Gaudi – Turkish art dealer builds home inside iconic tourist attraction - 20 Mar, 2019 @ 18:38
- Spain tops global health league but all is not well for expats - 19 Mar, 2019 @ 16:59
- Lady Elizabeth School, in Benitachell Alicante, is to have its grand inauguration this month - 19 Mar, 2019 @ 10:32
- How do casino promotions work in Spain? - 18 Mar, 2019 @ 14:05