Something from a bit later. Copy of a small section of cosmati floor, from about 12th century (about 25cm x 25cm). This pattern is known as Sierpinski's Triangle and is taken from the floor at Westminster Abbey in London.
The reason I post this up here is so you can see one of the main skills you need to develop in setting out geometric mosaics and that is knowing how far you can deviate from the key points of a pattern.
A quick search on the internet and you can find some wonderfully precise technical drawings of this sort of thing but trying to get the same precision on you actual floor is impossible.
You need to develop the eye to be able to see when the mosaic is too far off the key points but also to be able to see that although something looks quite scruffy close up it's ok to keep it like that. So long as when you step back you can see the pattern then don't worry about being too neat.