This is another example of La Tene styled artwork, which is merged again with some later style Celtic spirals. The La Tene swirls that are commonly seen on early metalworks and pottery actually evolved into the spiral forms we see commonly in later Celtic manuscripts like the Book of Kells and the Lindisfarne Gospels. The La Tene period in Celtic history dates from approximately 450 BC to 50 BC, and is names for the La Tene valley in Switzerland, where a large amount of early Celtic artifacts were found. These artifacts were patterned all in a similar style, and since then this style of artwork from this period is usually called the La Tene style of Celtic art. It's a very loose and organic style of art, characteristically full of tendril and loops, rather like plant life.