On the evening of 12 February 55 CE, a thirteen-year-old boy named Britannicus attended a dinner with his stepbrother, the Emperor Nero. His cup of wine was served hot, so a servant cooled it with water. According to the historian Tacitus, Britannicus immediately lost both his voice and his breath. He collapsed to the floor convulsing while the assembled guests watched in stunned silence.
Nero, entirely unhurried, told everyone present that the boy simply suffered from epilepsy and that they should carry on with dinner. Britannicus – the biological son of the previous Emperor Claudius, and a dangerous political rival – was dead before anyone left the table.
Behind that cup of water was a woman named Locusta. And her story is one of the strangest, most unsettling, and most revealing in all of Roman history.
A career built in the shadows
I always find it a bit frustrating when looking into figures like Locusta – we know next to nothing about her early life. The ancient sources, primarily Tacitus, Suetonius, and Cassius Dio, all wrote decades or even centuries after the fact. Tacitus and Suetonius were writing roughly sixty years after Claudius's death; Cassius Dio over a hundred and fifty years later. None of them had any interest in giving a convicted criminal a sympathetic biography. What they do agree on is this: she came from Gaul – broadly, modern France – she had developed an extraordinary expertise in plant-based poisons, and by 54 CE she was already sitting in a Roman prison, convicted of poisoning.
AI-generated depiction
It's worth pausing on that last detail. She wasn't recruited from obscurity. She was already notorious enough that when Agrippina the Younger – the wife of Emperor Claudius and quite possibly the most politically ambitious woman in Roman history – needed a poisoner, Locusta was the name she reached for. That infamy was, in its own grim way, her professional credential.
According to Tacitus, Agrippina had long been planning her husband's death. She wanted Claudius gone so that her son Nero could take the throne, and she needed a poison that was difficult to detect – something that might, as Tacitus puts it, derange the mind and delay death so that the cause wouldn't be obvious. Claudius loved mushrooms. Locusta prepared a compound that was slipped into the emperor's meal. The poison worked, though perhaps not quickly enough – later accounts describe a further dose being administered via a feather used ostensibly to help him vomit, though modern historians treat that particular detail with a healthy dose of scepticism. Claudius died on 13 October 54 CE. Nero became emperor at sixteen.
The art of being indispensable
Here is where Locusta's story takes a genuinely bizarre turn. You might expect that, having served her purpose, she would be quietly disposed of or thrown back in a cell. Instead, Nero kept her – not just as a free woman, but as a state asset. He pardoned her, set her up on a country estate, and, if the ancient biographers are to be believed, sent pupils to be trained in her methods.
Modern historians are fairly sceptical that Rome ran a literal, state-sanctioned school of poison-making – it reads more like a scandalous flourish by Suetonius, designed to illustrate just how comprehensively Nero had corrupted Roman values. But the fact that people believed it, and that it found its way into multiple historical accounts, tells you something about how untouchable Locusta had become in the popular imagination.
Nero's use of her was entirely transactional. When he decided that Britannicus needed to die – Claudius's biological son represented a standing political threat that wouldn't diminish as the boy grew older – he went straight back to the woman who had helped place him in power. The first poison Locusta prepared was too slow for the emperor's liking. Nero, never known for his patience, supposedly flogged her himself and threatened her with execution if she didn't do better. The next version was faster. It was this second compound, slipped into the cooled water at that February dinner, that killed Britannicus within minutes.
What's striking here isn't just the violence – it's the sheer transactional efficiency of it. Locusta wasn't operating in the criminal underworld any more. She was functioning as an imperial contractor, and the emperor was an impatient client.
The woman behind the sources
There's something important to acknowledge here, and it's a dynamic that always complicates ancient history. Almost everything we know about Locusta comes from elite male historians writing long after her death, men with their own political agendas operating in a culture where poison was understood as a specifically female weapon – cowardly, indirect, and entirely unbecoming of Roman masculine virtue. Locusta's existence was highly useful to Nero's critics. She wasn't just evidence of his cruelty; she was evidence of his unmanliness. A proper Roman emperor killed his enemies with legions, not a woman's herbs.
Does that mean she was simply invented – a Roman bogeyman conjured to make Nero look worse? Probably not. She appears across too many independent sources for that. But it does mean her story deserves to be read with an awareness that its tellers had motives beyond simple accuracy. Locusta has no voice of her own in the historical record. No letters, no testimony, no account of her own perspective. What we have is what her enemies said about her, filtered through what those enemies' enemies wrote down later.
That silence is worth sitting with. It's a reminder of whose stories got told in the ancient world – and whose didn't.
An ending carved in public
When Nero finally fell from power in 68 CE and committed suicide, the imperial shield that had kept Locusta safe for fourteen years evaporated overnight. His successor, Galba, set about dismantling Nero's regime with considerable enthusiasm. Cassius Dio records that Locusta was led in chains throughout the entire city of Rome before being publicly executed – alongside other members of what Dio memorably describes as the scum that had risen to the surface during Nero's reign.
There's something almost theatrical about that ending. Fourteen years of operating with imperial blessing, living on a country estate, being functionally untouchable. And then, chains through the streets.
I keep coming back to Locusta's story because it refuses to settle into a comfortable shape. She's not exactly a conventional villain – the people actually giving the orders were Nero and Agrippina. But she's hardly a simple victim either; the evidence suggests she was remarkably skilled at her trade and not obviously reluctant to practise it. She existed in a space that Roman society had no clean category for: a woman with a lethal expertise that the empire found absolutely indispensable, right up until the moment it didn't.
When we look back at the machinery of Roman power, we tend to focus on marble statues, senate speeches, and marching legions. Locusta is a reminder that empires run on a darker, quieter infrastructure as well. Running the ancient world, it turns out, required all kinds of specialists. She just happened to be one of the most dangerous.