Edinburgh Castle was placed on lockdown as activists broke open the case containing the Stone of Destiny.
Protest groups reportedly smashed the glass case housing the Stone of Destiny in a protest demanding action on Scotland's cost of living crisis.
Campaign group This Is Rigged claimed to be behind the attack.
The Stone of Destiny is an ancient symbol of the Scottish monarchy, used for centuries at the inauguration of its kings.
It was captured by the forces of Edward I of Scone during the English invasion of Scotland in 1296, and was used in the coronation of England's monarchs.
In 1914 it was damaged in a Suffragette bombing campaign which broke the Stone of Destiny in two.
The damage was not discovered until Christmas Day 1950, when a group of four Scottish nationalist students removed the sacred object from Westminster Abbey, intending to return it to Scotland.
During the rash raid, the stone was found broken. The group buried it at a campsite before burying a large portion in a field in Kent where they camped.
Despite the fact that the British state was searching for the lost object, the team managed to return it to the altar of Arbroath Abbey.
He was found by the Metropolitan Police just four months later and returned to Westminster.
But the theft sparked a growing debate about Scotland's identity, and in 1996 the British government announced the stone would be returned to Scotland – 700 years after it was first captured.
Today the red sandstone is one of the priceless treasures on display in the Crown Room at Edinburgh Castle. The stone is said to be leaving Scotland again for a coronation at Westminster Abbey.
A Police Scotland spokesman said: “At around 10.45am. we were called to a report of a small protest inside Edinburgh Castle.
“Officers attended and two women aged 20 and 24 and a 20-year-old man were arrested in connection with the damage caused.
“Investigations are ongoing.”
In March, This Is Rigged broke the glass holding Braveheart aka William Wallace's sword demanding an end to all new fossil fuel projects in Scotland.