Next Thursday, June 15, is a date of constitutional significance not just here but in every jurisdiction that adheres to the rule of law. It deserves to be celebrated as the fountainhead of liberty.

On that date, 808 years ago, Magna Carta – Latin for The Great Charter – was agreed to in a field at Runnymede near England’s Windsor Castle.

It started life as a peace deal between disgruntled nobles and a reluctant King John, one of England’s worst monarchs. But it became much more.

The peace did not last but the words of the Great Charter took on a life of their own. Over the years, the original 1215 document was copied, reissued and revised, culminating in a 1297 edition of which just four remain in existence.

The Australian government bought one of those 1297 editions in 1951, paying a mere £12,500 for an artefact that is truly priceless.

The real value is in its ideas. They marked the start of the doctrine which now means nobody is above the law – not even a king of England, a prime minister of Australia or an American president.

This idea underpins constitutional government in Britain, Australia, the US and other countries that share a common law heritage.

It marked the beginning of the doctrine of equality of citizenship – that all citizens should be treated fairly and equally. It also marked the starting point for the idea that government power should be limited, that human rights should be protected and justice should be accessible to all.

These concepts were once confined to England and subsequently to the Anglosphere. But they now form key parts of the benchmark by which governance is judged internationally.

In 1948, when the Universal Declaration of Human Rights came into force, it was described by Eleanor Roosevelt as: “The international Magna Carta”.

In 2015, the Federal Court’s Justice Stephen Rares told a meeting of the Judicial Conference of Australia that the Universal Declaration includes provisions that reflect the promises made centuries earlier in Magna Carta. These included the right not to be subjected to cruel, inhuman or degrading treatment or punishment, arbitrary arrest, detention or deprivation of property.

Other rights that Rares traced back to the Great Charter included the right to equal recognition before the law, equal protection by the law, the right to a fair and public hearing before an impartial tribunal in civil and criminal matters and freedom of movement.

The international impact of the Great Charter can be seen at Runnymede itself where a monument was erected by the American Bar Association, not the people of England. It bears this inscription: “To commemorate Magna Carta, symbol of freedom under law.”

Americans, like Australians, owe much to the Great Charter. In the eighteenth century its ideas informed the resentment of American colonists over what they considered to be the predations of the British Crown.

The same ideas helped Australian colonists in the nineteenth century transform this country from a penal colony to a free society.

The late Tom Bingham, a former lord chief justice of England and Wales, has pointed out that it was natural for American revolutionaries, in resisting what they saw as the unlawful pretensions of the Crown, to rely on Magna Carta, treating it as a higher law that the Crown could not defy.

The same ideas, bolstered by constitutional developments in England, arrived in Australia with the First Fleet.

In his book, The Rule of Law in a Penal Colony, David Neal writes that the political ideas and language that Australian colonists drew upon, both for struggles among themselves and against the metropolitan power, were based on their English legal inheritance.

“Rather than the universalist, abstract language of the French and American revolutions, they claimed no more than their rights as free-born Britons, rights guaranteed by the Magna Carta, Habeus Corpus, the Bill of Rights, the Act of Settlement and the great synthesis of that inheritance, Blackstone’s Commentaries,” Neal writes.

In 1788, those who waded ashore at Sydney Cove included two convicts, Henry and Susannah Kable, who successfully sued the master of their convict ship over the loss of a parcel containing their possessions.

It was Australia’s first civil case and it proved that equality before the law was part of this country’s heritage from the very beginning. It is a doctrine that for too long was applied imperfectly.

Yet even in the dark days when it was reduced to a mere aspiration, the desire for equal treatment never disappeared and helped inform the long struggle to build a nation based on the idea we are all equal regardless of race, religion or political affiliation.

Equality before the law can be traced all the way back to Runnymede. But this principle could be rendered meaningless unless it is accompanied by two other ideas: equality before those who make the law and equality before those who administer it.

This is what is really at stake in the coming referendum. When it comes time to vote, we should remember what happened 808 years ago, and the surprising courtroom victory of two convicts.

The Kables might have lost their possessions, but they had something far more valuable: a legal principle that came ashore with the First Fleet. It should not be lightly discarded.