The writing was on the wall for many of the prisoners incarcerated in the Tower of London over the centuries. Now, it can finally be deciphered.

Hundreds of graffiti texts scratched into the historic stone walls by prisoners as they awaited their fate have come to light for the first time. Examples that were either overlooked or illegible are emerging through cutting-edge technology.

Dr Jamie Ingram, who is heading a major project to study graffiti in the Tower of London, described the discoveries as “exciting”. He began studying the Salt Tower on the south-eastern corner – part of the curtain wall that Henry III built in the 1230s. Its prisoners included Hew Draper, a Bristol innkeeper accused of practising sorcery and imprisoned in 1561, who carved an astrological sphere with zodiacal signs into the wall, despite having claimed that he had destroyed all his magical books. No record exists of his fate.

Ingram told the Observer: “There were supposed to be 79 examples of graffiti there, according to the historic survey. By the end of the survey that I conducted, there are 354. Very fine viewing of the surface of the walls has allowed us to identify what else is there … acknowledging that every mark is important, rather than just those that have been left by the famous prisoners.”

The Tower of London, a secure fortress and royal palace, has held prisoners including the two princes, Edward V and Richard Duke of York, Anne Boleyn, her daughter Princess Elizabeth, and Guy Fawkes. Today it is managed by Historic Royal Palaces, an independent charity, which Ingram joined last year specifically to research one of the UK’s most significant collections of historic graffiti.

The latest technology, which includes raking light, laser scanning and X-ray analysis, has never been applied at the Tower before. “Light shone off at an angle … enhances the creation of shadows on that surface and lets us really see the detail,” Ingram said. “As soon as we bring these modern methodologies to bear on it, things start to change quite dramatically, and suddenly we can actually start to read it.”

One section of a wall bears graffiti by possibly three hands. The dates 1571 and 1576 are also inscribed. These had been listed as “illegible”, but are now being deciphered. While the complete texts have not survived, certain words can be picked out.

One of the passages seems to be in Breton and may well have been written by a woman. There are references to a “husband”, as well as honour and rivers. Ingram said: “We haven’t got any specific records of female prisoners in that tower. This is possibly a woman’s voice, which is incredibly rare in the graffiti, and the first example we’ve got in the Salt Tower itself.

“We know that there were women at the tower. They’re just not represented in these physical first-person records. This is a rare primary record of a woman’s presence, whether she’s a prisoner herself or the wife of the prisoner.”

Most of the graffiti is pictorial, including crosses, which reflect that “a lot of religious prisoners [were] held in this space,” he said. Most of the texts are relatively short and include biblical passages.

Funding for the graffiti study has been made available by a private donor. . Ingram will next focus on the Byward Tower, at the south-west corner of the complex. He said: “There’s some amazing graffiti in there that’s going to allow us to ask some more questions.”

But he expressed dismay that today’s visitors are adding their own: “If they’re doing it with a pen or pencil, there’s no evidence that it’s being done until it’s too late. Where we can, we clean it off [but] it gets into the stone and damages it. It’s horrifying that they’re doing it on a monument so significant to us.”