On Tuesday, that Union is under threat again, as the First Minister Nicola Sturgeon prepares a new push for a second independence referendum.
Seeking another vote in October next year, she will argue that Westminster is “taking a wrecking ball to the idea of the United Kingdom as a voluntary partnership of nations” unless the Scottish people are allowed to decide their future all over again.
Last time, as Scotland prepared to vote in 2014, the Queen made a rare intervention.
In comments royal experts have argued about ever since (were they as pointed as they sounded? Did she intend for them to be heard?), she spoke , I hope people will think very carefully about the future."
This week, as the SNP seek to overturn it, the Queen will make no such comments.
Instead, her mere presence will be a reminder of all she stands for: continuity, tradition, and that hard-to-define relationship between the Queen and her people.
All week, members of the Royal family will put on a show of force, from a full military parade for the Platinum Jubilee to a church service, investitures and tea-and-scone-filled garden party.
The timing on their part is a genuine coincidence: the week happens each year regardless of what is happening in Scottish politics.
But the Queen did not have to attend.
Having missed a succession of high profile and previously annual events in the royal calendar as a result of well-documented mobility issues, there was almost no expectation that she would be there in person.