Detail from a mosaic at the archaeological museum in Barcelona, Spain, 2 -3rd century AD. Two things to see here, the red square (A) shows the difference in tesserae size. The line (B) shows how the circle in the pattern should go but it has been interrupted by the lines of black tessere.
1. Was the border put in later and why use larger tesserae for it? Were the tesserae used for the border left over from another floor?
2. Did they just miscalculate the space needed and they couldn’t fit in the rest of the circle or was it intentional?