A short story. Made up, like the others.

The mosaic floor came out of a Roman villa under a farmer’s field in 1962, and it spent the next sixty years in the museum basement, in eleven pieces, each one set in a slab of concrete. That was how floors were lifted then. You glued cloth to the face, cut the floor into sections, levered each one up and poured concrete on the back. It kept the pieces together, and it made each one weigh as much as a car.

My job was to get the concrete off, put the pieces onto light honeycomb panels, and lay the floor again in the new gallery, in time for the opening in March.

The middle is a head of Neptune with a lot of seaweed in his beard. Round the outside is a border of running wave, the pattern that looks like a line of breakers all curling the same way, black on white. It’s the part most people walk past. It’s the part I like. It’s very hard to set a running wave round four sides of a room so that it comes out even at every corner, and whoever laid this one did it.

On the north side there was a gap in the border about thirty centimetres long, where a few hundred tesserae, the little stone cubes it’s made of, had been lost. Probably in the lifting. The edges of the gap were the clean edges of a saw cut, so it was likely somebody’s chisel slipped in 1962 and that bit came up in crumbs.

Ruth, the director, wanted the gap filled. “It’s a wave,” she said. “It goes wave, wave, wave. You can see exactly what goes there.”

I could, more or less. Two more waves, the same size as the others, would fit. But the rule I work to is old and short: restoration stops where conjecture begins. I’d fill the gap with plain mortar, toned to sit quietly, and anyone who wanted to could finish the pattern in their head. Ruth said visitors don’t cross town to look at mortar. We left it there.

To put the eleven pieces back in the right places, I needed the excavation photographs. They were in a box in the archive room, black and white, a lot of men in jumpers. One was taken from a ladder before anything was lifted, the whole floor at once, with a striped surveying pole laid along the north side, marked off in feet.

The gap wasn’t a gap yet. Where I’d have put two waves, there were three. They were smaller than the rest, squeezed, the curls tighter, packed into the space of two. On either side, the border ran on at its proper size. Smaller waves mean smaller stones and more mortar between them, which may be why that was the bit that crumbled.

I measured it against the pole, then measured the other three sides on the floor itself. They were all fine. The north side had been set out short, by about one wave, and whoever was laying it must have found out partway along. He could have let the pattern run on and break at the corner, where everyone would see it. Instead he took up the difference here, a third of the way along, in a foot of slightly crowded waves, and the corner landed exactly. The photograph shows it landing.

So the obvious answer, wave, wave, would have been wrong. And it would have rubbed out the one place on the floor where you can see somebody stop and think.

A photograph isn’t conjecture, though. I made the three small waves from the photograph, in new stone, cut to match and set a hair lower than the old, so they catch the light a little differently and anyone who looks closely can see where his work stops and mine starts. It took most of February.

Ruth came down to see it a week before the opening. She stood at the north side for a while.

“Those ones are wrong,” she said.

“They’re the right ones. He ran short.”

“Who did?”

I showed her the photograph. She held it up and looked from it to the floor and back. “Well,” she said. “So he did.”

The other thing about February was that the plinth the floor sits on had been built two centimetres shorter than the drawings, which is the sort of thing you find out when the last panel won’t go in. Two centimetres has to go somewhere. The saw cuts had left the joints between panels wide anyway. You take it up in those, a few millimetres in each, or all in one, where nobody will look.

I took it up in the joint beside his three small waves. You can’t see it unless you know. But he’d have known.