What we call a Mosaic Tile today is very different to the mosaic tiles of the past. In the beginnings of mosaic art, tiles were very inconsistent in size and shape and even color. They were basically hand cut pieces of clay pottery, cut stone or even just found pebbles. Although many great works of mosaic art were created in the past, for our modern requirements, we obviously need a much different form of tile.
Luckily for us, modern technology has got to a point were we can mass produce mosaic tiles very consistently. The size shape and color differ very little in comparison to the the tiles the average Roman craftsman would have to work with!