Vintage Decorative Plate or Platter

I picked up this highly unusual vintage plate at recent estate sale and curious if anyone knows anything about it? It is very heavy and extremely ornate. The white dots are also raised. Appears to be hand-painted. There is much texture to the front of the plate itself but has a smooth glaze over finish in the back. Weighs slightly over 2 lbs. Measures approximately 10” x 13”. I don’t see artist name anywhere on the plate outside of a strange mark on the back but it does look quite old. Hope someone might be able to help me identify it and tell me what this item may be. Not sure what the scene on the plate is a depiction of. Comes across as having a Christian theme, but I could be wrong. Three of the four figures appear to be bowing down to the person in the center, a king perhaps, due to the purple robe. And one of those three also appears to be praying. The person standing in the center seems to be holding up a vase of sorts with fire coming out of it. These thoughts come to mind - Crusaders, Templar, Medieval, King Richard, Holy Grail, perhaps English origin?