In our ante room we have designed a ‘best of Roman Somerset’ mix of mosaics. First up is a colourful guilloche border, copying a design from the cold plunge pool at Lufton villa. On the original there are some wonderful fish but it seems like 2 groups of mosaicists worked from opposing ends and only realised when they met, that they had been doing a different design and going in opposing directions. The bodge work around was to put in a black and white zip join. Its nice to imagine the conversation they had with the villa owner. We may suddenly change colour on our design part way around, as a nod to the incompetence of our predecessors.
'Hands on Heritage' in the Avalon Marshes 
It might not have been incompetence on the part of the Lufton mosaicists. Maybe it just didn’t matter to the proprietor? We can’t judge by modern standards and preferences. The Lufton fish are wonderful and seem quite happy with the arrangement!
It would have been easy to get the guilloche to all go in one direction without the awkward join, so I find it hard to believe it was planned. Starting the design in several places would make sense in terms of getting many people working at once and gettings the direction conflicting from the start would be a very easy thing to do and perhaps only noticed at the end of the day, and you don’t want to redo a whole days work
Not suggesting it was planned; just that it might not have mattered from the outset. We need a Dr Who-type Tardis to go back in time and ask whether it was a mistake they decided to live with – or whether the concept of mistake would baffle them! Your project is great at providing food for thought!
You’re right that we can’t know for sure, but its been good doing the mosaic because its shown the sorts of things that can easily go wrong, especially if you think they must have been laying the mosaics at speed to maximise profit. There are lots of little mistakes in Roman mosaics in the UK, which you only notice if you are deliberately looking for them, which we do to make ourselves feel better. The difference is that we corrected or errors when we spotted them but the Romans didn’t bother, as generally they would have gone without notice by the client.