I was amazed. 'What? No arsonists or balcony-thieves? No drunks, muggers or raucous insulters of frail elderly women? Can this be Saturnalia? Whatever has happened to riot in the streets?'

'We had a bunch of house guests, Falco. I personally supervised letting them all off with a caution. In return I have a pile of promissory notes several inches high. The riot begins officially tomorrow,' said the clerk. Then he explained why he was the only person left in the station house, and why even he was about to lock up and leave. 'Tomorrow we'll need every man on the streets: no leave, no sick notes, no stopping at home with toothache without a sick note, and no bunking off to your grandmother's funeral for the fourth time this year. Tomorrow is mayhem, and we'll be there. Tonight, therefore, is the Fourth Cohort's Saturnalia drinks party.'

I said they would all be there tomorrow with dreadful hangovers, then – and he said, he couldn't wait around any longer, so did I want to come? I should have gone straight home. I knew it. I had managed to avoid this particular event in the calendar for several years, but I was well aware of what went on. Those who attended always spent the following twelve months reminiscing about it. They would have longing looks as if they wished they could remember the best bits: what the raw recruit had innocently said to the tribune just before they both passed out and why the bill for breakages had been so high. I had been joking when I told the clerk that the troops would all be on duty tomorrow with bad heads. Most would not reappear at the patrol house for about four days, and when they turned up, ashen and trembling, it would take several hours of pep talk, stomach-settlers all round from their doctor Scythax, and a bought-in breakfast to remove the sedative effects of the stomach pills, before the situation that the innocent public know as 'on duty' could possibly occur.

I was too young for this. I had too many responsibilities. I should have run a mile from the legendary night of degeneration – but I did the same as you would have done: I let him lure me into it.

XXXIII

I was led to a large, unused warehouse. I told myself nothing could go wrong; after all, my sister – the virtuous, pompous one – was in charge of the catering.

A cohort of vigiles is about five hundred strong. Sometimes there is a shortfall, with a group on detachment to guard the corn supply at Ostia, but the Fourth had recently finished a tour of duty there. It is just like the army: on a good day, ten will be laid off with wounds (more after a large building fire, many more after a major city conflagration), twenty in the sick bay with general illnesses, and fifteen specifically unfit for duty due to conjunctivitis. The treasurer has always gone to see his mother. The tribune in charge is always present; nobody can get rid of him, whatever devious ruse they try.

The first sight to greet me, then, was Marcus Rubella, the Fourth's untrustworthy, over-ambitious cohort tribune. He was standing on a table, with his shaven head thrown back, draining the biggest double handed goblet of wine I had ever seen. In a gathering of blacksmiths or furnace stokers, who are the world's heaviest quaffers, this would have been the final stunt of the evening, after which everyone would collapse. Normally a loner, whose men had yet to learn to like him, Rubella was just warming up in between raiding the early canapй trays. Occasions like this were when he did win the vigiles' wary respect. After a handful of quails' eggs and a few oysters, their hard man would accept some other drinking challenge, remaining vertical and apparently sober throughout. The vigiles could admire that. It deserves mention that in order to show how conscientiously he threw himself into occasions of cohort festivity, Marcus Rubella (a staid man, conscious of his dignity) was currently wearing a silly hat, winged sandals and a very short gold tunic. I noticed with a shudder that he had not shaved his legs.

Of the five hundred men who nightly patrolled the Twelfth and Thirteenth Districts, almost every one was there. The sufferers from the sick bay had bravely rallied. Even the bucket-handler with life threatening burns from a bakery fire had been carried in on a stretcher. Someone whispered to me that he had struggled hard to last out until the party. If he died tonight, he would be smiling.

A drink found its way into my hand. I was expected to gulp it as fast as I could then have more; my elbow was jogged as encouragement. I recognised the wine as vinum primitivum from that night at Flora's. Then I spotted my sister Junia, red-faced and harassed as she pushed through the press. She was approaching forty and the menopause, but that hadn't stopped her pinning her hair in fat, lopsided rolls, adorning the edifice with fake rosebuds, and mincing about in her second-best stole. The effect was incongruously girlish. I felt slightly sick. 'Oh Juno, Marcus, these men are voracious – I'm never going to have enough!' 'You knew what you were taking on. You've heard Petro rhapsodising often enough.' 'I thought you and he were exaggerating as usual.'

'Not this time, sis!' Fear grew in her eyes. Grinning, I let her be dragged away by a group who were demanding their mixed platter of seafood (they knew exactly what they had signed for when the menus went round for advance orders) – what did it take to get service? they had asked four times… The vigiles held one party a year and were as fussy as young patricians at an expensive banquet. More so, because the vigiles paid for theirs.

When plain men who do hard jobs hold an entertainment, they like all the trimmings. Whole trees had been suspended from the rafters, until the roof space was crowded with greenery. Dropped pine needles stuck through the gaps in your bootstraps every time you took a step. Beneath the aromatic forest canopy, they had positioned enough lamps and candles to chase away the darkness of Hades. Smoke from the oil and wax was already thickening the air. Sooner or later they would set something on fire; in theory they had enough professional know-how to douse the blaze – but that assumed any of them were still sensible by then. Already they had flushed faces, gleaming with sweat from the heat and excitement. The noise level had risen high enough to cause complaints from neighbours several streets away – though if the locals had heard that this party was being planned, they had probably all left to stay with their aunties in the Sabine hills.

At one side of the room, a long table was serving as a bar. The idea was to protect Apollonius, who was penned behind it, looking unperturbed as he diligently doled out pottery cups of primitivum from a vast row of amphorae. The hard-bitten drinkers in the cohort had wedged themselves three deep in front of the table where they could most easily grab refills, and were set to stand there all night. Fighting fires gives men a great capacity; the vigiles were practised in working up a thirst. They had been banking contributions to the food and drink bill for the past twelve months, after which Rubella had added his customary top-up. He liked to pretend the bags of sesterces were a personal contribution, a generous thank-you to his loyal men; in fact, we all knew he fiddled the equipment budget. Still, he took the risk, and if ever the cohort was properly audited it was Rubella who would be penalised… Unlikely. I could see the internal auditor lapping up wine in a corner with a blissful expression that had nothing to do with discovering financial irregularities. He looked as if he had come across a crock of gold coins buried under a thorn-bush, and wasn't going to give the treasure back to its owner.

Quite a few of the vigiles were in fancy dress. They must have borrowed costumes from a third-rate theatrical troupe, the kind that drew the crowds the intellectual way: notoriety for topless actresses. The fire-fighters were sturdy ex-slaves with arms as thick as anchor cables and chin stubble a bear would be proud to own; in flimsy drapes of turquoise and saffron, the results were unspeakable. Some were throwing themselves into their feminine disguise so wholeheartedly it was sinister. Others were more restrained and had merely crammed wreaths on their greasy heads or draped themselves in strips of moth-eaten fur. Three were pretty well naked and had spent all afternoon painting one another all over with blue patterns, to look like Celts in woad – always a popular obsession in Rome. One of them had mistletoe in his hair, while a second had made himself a torque, though the 'gold' had melted and was running down over his swirly patterned chest among the curly black hairs and sweat. Attending on Rubella I saw a man dressed as a splendid five-foot carrot. His friend had come as a turnip, but had taken less trouble and didn't look so good.