zitrooona ⋆ ⁺₊⊹ 🌺@aaronsgiles I'm relatively sure this is an element of the "Diptych of Rambona", an old ivory carving (top right quarter, 1st attached photo). I found a replication of that Celtic knot as a brooch through an eBay listing, see the 2nd image attached below.
If you rotate your image (a postcard for your bot I'm guessing? 😁) by 90° clockwise, it'll match the brooch. I'm assuming the image is either a very heavily edited photo, or it's a 3D scan, possibly the one that was used to create the brooch.
You can find a detailed description of the carving on Flickr and a high quality photo of it on Wikimedia commons
All GNU social JP content and data are available under the ,_south-central_Italy,_c._900_AD,_ivory_-_Vatican_Museums_-_DSC00716.jpg){kind=link}