My personal idea is that they are objects created both to flex metalworking craftsman skill and in worship of sacred geometry. Ancient peoples ascribed divinity to the harmonies of the universe, especially the harmonies in mathematics like geometry. The fancier looking platonic solids like dodecahedron and icosohedron have almost magical levels of symmetry built in to them making them both aesthetically pleasing complex shapes. The fact they even exist inspires philosophical and even spiritual thoughts. As far as I understand romans had some very impressive archetecture incorporating mathematical ratios almost constantly, archetects and metal workers may very well have needed to worship geometry as a divine aspect in order to achieve such neurotic levels of mathematics in their aesthetic.