They tried storming it with troops, starving its inhabitants, catapulting missiles over the walls and scaling its ramparts.

Pevensey Castle, one of the oldest in Britain, withstood sieges and attacks for 1,000 years.

During medieval times its Inner Bailey was besieged no fewer than four times yet it was never successfully overrun by direct assault.

Even in the last century it was considered strong enough to turn into a war-time fortification. Its 12ft-thick walls made it attractive enough to be a command post against any invading Germans during the Second World War.

But its reputation as one of the country's most impenetrable fortresses ended this week. The successful intruders were not invaders or armies led by a pretender to the throne.

They were vandals.

Youths somehow breached or shinned up over its 50ft-high walls and attacked a kiosk-cum-gift shop inside the Inner Bailey. They jemmied open a security shutter and smashed a window - all for just £3 worth of Roman and Second World War toy soldiers.

Allison Muir, head custodian at the castle, is less than happy and has a medieval punishment in mind.

Hidden under a north tower next to the castle gate house lies a 15ft-deep hole in the ground.

Called the Oubliette, a French term meaning forget, it was used to house prisoners. Those worth keeping alive for ransoms were lowered down by rope into the dark, damp dungeon. Others were thrown down and forgotten. Ms Muir, who has loved every minute of her 12 years working at the castle, said: "I'd like to throw whoever did this down the Oubliette."

And she is only half joking: "This castle belongs to the country so when something here is smashed or broken everyone is paying for the repairs. I have a great love of the castle and it hurts when people abuse it like this."

Romans founded the great fort of Anderida, where the castle sits, towards the end of the third century. It was overwhelmed by Saxons in 491, when every single defender was said to have been slain, but the more modern Inner Bailey remained impervious.

The castle was deserted for years until William of Normandy landed at Pevensey and his half brother built an earth and timber castle on the site.

This week's "assault" on the castle happened some time between 7.10pm on Tuesday and 9.10am on Wednesday. Sussex Police appealed for witnesses or anyone with information to call them on 0845 6070999.