SALISBURY, England — The corgis just wouldn’t behave. Mid-take, they ran off, causing general hilarity. “Sit, sit!” Olivia Colman called out.

“Strong voice!” prompted the dog handler, standing nearby.

“Yes, thenk you,” said Colman demurely, in her best Queen Elizabeth accent. She frowned imperiously at the frolicking dogs. “SIT!” They sat.

It was a chilly November day last year, and the new cast of the Netflix series “The Crown” were arrayed across the gilded couches and crimson velvet chairs of a sumptuous state room at Wilton House, a 16th-century stately home standing in for Buckingham Palace. A precisely composed group — the Queen (Colman), Prince Philip (Tobias Menzies), Lord Mountbatten (Charles Dance) seated; Princess Anne (Erin Doherty) and the Queen’s aide Michael Adeane (David Rintoul) standing behind them — faced Prince Charles (Josh O’Connor). Like the central figure in the van Dyck painting of an aristocratic family hanging behind him, Charles cut a lonely, isolated figure, setting the tone for an episode in which he is obliged to leave university in Cambridge, and go to Aberystwyth to learn Welsh, in preparation for his investiture as Prince of Wales.

With its artful interweaving of British history and domestic angst, the scene was vintage “Crown.” Created and written by Peter Morgan, the series has spent two acclaimed seasons exploring the nation’s politics and social mores through the prism of Queen Elizabeth II’s reign, while offering a voyeuristic glimpse of the lives behind the royal family’s impassive facade.

The eagerly awaited third installment of “The Crown” debuts Sunday on Netflix, and much will be familiar: the exacting historical detail, the sumptuous interiors of palaces and manor houses.

But one major aspect will not. The actors who play the principal characters have all been replaced for Seasons 3 and 4.

It’s the first manifestation of what has been the show’s plan from the beginning: to regularly recast Elizabeth, Philip and other royals to better reflect the characters’ advancing ages.

“I think that the longest you can believe an actor in an aging part is about 20 years,” Morgan said in a telephone interview. “Right from the start, we decided that if it all worked and kept going, we would recast every two seasons.”

“A great many changes, but there we are,” Elizabeth says, swatting away an underling’s compliments. “Age is rarely kind to anyone.”

The swap is also something of a gamble for a series that achieved rapturous acclaim for its principal actors, notably Foy, who won a Screen Actor’s Guild award and was nominated for an Emmy. But Morgan and his producers found a pretty sure casting bet in Colman, who is adored by the British public, and last year found broader fame when she won an Oscar for her portrayal of another English queen (Anne) in “The Favourite.” (There is at least one person who didn’t approve of the choice: Charles Moore, a well-known journalist and Margaret Thatcher biographer, wrote in The Daily Telegraph that Colman’s “distinctly left-wing face” made her unsuitable for the part.)

“Olivia has a similar, uncannily intuitive understanding of the role, and a stillness that Claire has,” Suzanne Mackie, an executive producer on the series, said in a telephone interview. “They feel like everyday women, that we should somehow know them, yet as they become the sovereign, they become unknowable and aloof.” (In a review of the new season, The Independent wrote that “there is something dazzlingly banal” about Colman’s portrayal of Elizabeth.)

Colman, who plays a more experienced ruler with a chillier, more confident mien, said in a sit-down interview last fall that she was trying not to think about following in Foy’s footsteps. “I am a massive fan; Claire was just breathtaking in that part,” she said. Sounding rather like her character, she added, “But you just plow on.”

Ben Caron, a director and executive producer on the show, said in a telephone interview that it had been “pretty terrifying” for the new cast. “Not only do you have the real-life ghost of the character, you have the ghost of the previous actor,” he said.

Helena Bonham Carter, who took over the role of Princess Margaret from Vanessa Kirby, echoed that sentiment. “My first thought was that I don’t look much like Margaret and definitely nothing like Vanessa,” she said in a telephone interview. “I am about five feet shorter and two feet wider. But they didn’t seem perturbed.”

After reading some of the scripts, she said, she was captivated by Margaret’s complexities and contradictions, and she embarked on a period of “forensic” research, meeting friends of the princess and working through a list of books that Kirby had recommended.

“It’s very dynamic to be able to capture different aspects of a character through different people,” she said. “And I loved taking over the part from Vanessa, who was a huge help to me. We could compare notes and say: ‘What about this? How would she react to that?’”

(Sometimes there were more practical problems with the cast changes. The production initially attempted to use contact lenses and special effects to change Colman’s and Bonham Carter’s brown eyes to blue, like those of Foy and Kirby. “But then it didn’t feel like the actors we loved,” Caron said. “So much of their performance is through subtle facial expression that we decided to just live with it.”)

“The Crown” is both essentially historically accurate and also clearly fiction. “It’s not a documentary,” Morgan said. “But I try to make everything as truthful as possible even if I can’t know it’s entirely accurate.”

Or as Erin Doherty, who gives a memorably acerbic portrayal of the young Princess Anne, remarked on-set between takes: “After a while you have to drop your thoughts about who they are — you have to accept we are Peter Morgan’s royal family.”

“The Crown” was conceived from the start to span six seasons, each covering roughly a decade of Elizabeth’s life as a monarch, and it is Morgan’s particular take on each season’s epoch that has given the series its distinctive mix of the personal and the political.

Season 3 begins with the election of Harold Wilson and a Labour government in 1964 and ends with the Queen’s silver jubilee celebrations of 1977. Along the way, it layers globally monumental moments, like the 1969 moon landing, with lesser-known national events (the horrific avalanche of coal waste in Aberfan in Wales, which killed 116 children and 28 adults); political intrigue (the miners’ strike of 1973-74); and family drama, including the breakup of Princess Margaret’s marriage to Lord Snowdon and the thwarted romance of Prince Charles and Camilla Shand.

Each episode could be watched as a stand-alone drama, with overlapping plots that resonate in unexpected ways; these correspondences and echoes give the show its emotional heart, Morgan said. “Mapping out the season is the part I like best.”

Before writing begins, Morgan spends six months on a detailed timeline of the period that includes significant royal milestones like marriages and deaths, as well as major political and social events. Once Morgan has begun to write, a bigger team, including researchers, script editors and producers, are closely involved in the process.

“While we were making Season 3, we were probably at Peter’s house most days,” Mackie said. “It’s not enough to have the historical facts of the story; you have to find where the tension, the human side might be. When Charles goes to Wales, for example, it becomes not just about a young man learning Welsh for political expedience, but about a young man finding his own voice.”

Morgan said that when he considers an episode, he ponders what might have “intimately intersected” with the Queen. “You think about the Kennedy assassination, Carnaby Street, but what is the connection there?” he asked rhetorically. “But when I discovered that the astronauts from the moon landing had come to visit the palace with terrible colds, that was priceless.”

“At first you have all the same ideas as everyone else about the decade,” he added. “It’s like running a bath in an old house; at first all the rusty water comes out, then the clear.”

The moon-landing episode focuses strongly on Prince Philip, with a tour-de-force performance from Menzies as a man suffering from a crisis of identity, for whom the astronauts’ achievements come to represent his own missed chances. Other episodes focus on Princess Margaret, and the later part of the series gives considerable weight to the young Prince Charles, sympathetically portrayed by O’Connor as a sensitive and insecure young man at odds with the implacable imperatives of royal behavior.

“There is a difficult moral question at the heart of his life,” O’Connor said in a telephone interview. “Being a king in waiting means waiting for his mother to die.”

But the Queen is always the center of gravity, Morgan said. “Every time I try to write an episode that doesn’t involve her, it runs aground.”

What is different in Season 3, he added, is that “it has gone from being a story about a woman finding her way, navigating with her partner, to a woman at the heart of a family drama. I look at ‘The Sopranos’ or ‘Succession,’ and think, they are just different versions of what we are doing.”

Morgan said he tried not to write with a sense of retrospective knowledge of, say, Brexit. (In Episode 8, the Queen goes to Paris to petition President Georges Pompidou to allow Britain to join the European Union.) “I think the minute you write prescriptively, it loses power,” he said. He paused. “But there are times. In Episode 10, Philip makes a speech about politicians and I probably gave that one coat of extra paint that might angle towards the complete failure of the political class at the moment.”

But for the most part, he said, “what writing ‘The Crown’ teaches you is that Britain has been in a permanent state of crisis. We talk about a divided country, here and in the U.S., but moments of unity, when the majority of the country is in agreement, are really rare. We invent a settled past.”

But as Morgan wrote in his 2013 play “The Audience,” which inspired the series, the reigning monarch represents “an unbroken line, the constant presence” that represents that settled past and serene future. That’s the power of the crown — and “The Crown.”