"Brilliant, Pa. So there won't be an access point for crawling under this floor."

"No. The only way in is down."

Nice work. We would have to break up the mosaic we had only just taken over brand new.

The under floor space in a usable hypocaust would be eighteen inches high, or two feet at most, with a mass of tile piers to support the suspended floor. It would be dark and hot. Normally they send boys in to clean them, not that I would inflict it on a child today- to face who knew what? I was relieved there was no formal access hatch. That saved me having to crawl in.

"So what do you think about this smell, Marcus?" my father asked, far too deferentially.

"The same as you. Your Neptune is; floating on rot. And it's not going away."

Instinctively we breathed. We caught a definite hum.

"Oh Titan's turds."

"That's what it smells like, Pa!"

We ordered the furnace slave to stop stoking. We told him to go to the house and keep everyone else indoors. I fetched pickaxes and crowbars, then Pa and I set about ruining the sea-god mosaic.

It had cost a fortune but Gloccus and Cotta had produced their usual shoddy work. The suspended foundation for the tesserae was far too shallow. Neptune, with his wild seaweed hair and boggle-eyed attendant squids, would soon have been buckling underfoot.

By tapping with a chisel, I identified a hollow area and we set to. My father got the worst of it. Always impetuous, he put his pick in too fast, hit something, and was spattered with foul yellowish liquid. He let out a yell of disgust. I leapt back and stopped breathing. A warm updraft brought disgusting odours; we fled towards the door. Judging by its powerful airflow, the under floor system must never have been blocked ofF completely as Pa ordered. We were now in no doubt what must be down there.

"Oh pig shit Pa peeled off his tunic and hurled it into a corner, splashing water on his skin where the stinking liquid had touched him. He was hopping with disgust. "Oh pig shit pig shit pig shit