Eureka hero John Joseph was largely forgotten in an unmarked grave

"On the drive here I wondered what John Joseph would have made of this scene, of people travelling near and far to commemorate his legacy," Santilla Chingaipe said.

"It's hard to know."

Chingaipe followed the Eureka hero's life for Our African Roots, a 2021 documentary tracking forgotten trailblazers who helped shape Australia before vanishing from our national conscience.

She is unable to say whether anyone close to Joseph attended his burial in White Hills Cemetery in Bendigo in 1858, or if it was a dignified send-off.

"Was he eulogised? And did his loved ones in America ever find out about his death or even about his life in Victoria?" Chingaipe asked.

"With no known descendants here in Australia and scant details about him outside of the Eureka Rebellion within the archives, much of who John Joseph was remains a mystery."

That was the "compounding tragedy" of Joseph's life, and others like him, Chingaipe said.

"They for so long have gone forgotten, erased or silenced because of racism," she said.

Historian, author and member of Eureka Australia, Geraldine Moore, said ethnicity may well have played a role in the forgetting of Joseph.

"Partly it's because he was black, partly it was because he did not live very long after Eureka - there were annual get-togethers by some of the participants in later years," she said.

Both factors made Joseph's legacy vulnerable when people began downplaying Eureka itself in a fit of imperialism around the time of World War I, Dr Moore said.

"There was this great outpouring of loyalty to 'King and Country' and it wasn't fashionable to have ancestors who had taken up arms against the Crown," she said.

What is known is that Joseph likely jumped ship like many others when the Gold Rush erupted in 1850s Victoria.

"He's described as a tall and powerful man of African descent, who was likely a sailor from the United States," Chingaipe said.

"Exactly how tall, we don't know. And depending on which source you look at, his hometown is listed as either New York, Baltimore or Boston."

He sold grog from his tent at multiple goldfields and in November 1854 had set up in the Ballarat Stockade.

"We can only guess at John Joseph's motives for joining disaffected miners when they finally revolted against the extortionist licencing fees and bullying tactics of police," Chingaipe said.

Whatever those motives, his involvement was more than simply a product of his own place and time, US Ambassador to Australia Caroline Kennedy told the gathering.

"It's also a story for our time," the daughter of American president John F. Kennedy said.

Ms Kennedy's arrival at the cemetery had earlier sent a ripple of silence upon the gathering of dignitaries, historians, Eureka descendants and media.

Her family's links with the transformations of African Americans' lives more than century after Joseph's death reverberated even in the White Hills cemetery.

When journalists - including from the New York Times - scrummed following proceedings they did so with a larger crowd.

"Ambassador Kennedy?" one man with an American accent said as local journalists asked questions.

"I just wanted to thank you, from all of us Black Americans, back in America, for taking that leadership step ... you are awesome, we love you. Thank you."

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Ms Kennedy had earlier told the crowd that Joseph's story might be a product of his time and place "but it's also a story for our time".

"Americans can be proud John Joseph played a pivotal role, proud of his courage in the fight and his role in the trials and their aftermath," she said.

"But we must also acknowledge the American context at this stage."

In the same year Joseph fought at the Eureka stockade, extreme race-fuelled violence was breaking out in America, Ms Kennedy said.

The US Congress was allowing the extension of slavery into new states in a key moment pushing America towards civil war.

In Victoria, the American consulate refused to help Joseph despite aiding other Americans caught up in Eureka. The constitutional rights that protected Joseph's countrymen simply did not extend to him.

"We can ask ourselves, who is missing from today's narrative? What is our responsibility to make sure they are included?" Ms Kennedy told the gathering.

People could take heart at the progress made in places like Australia and the US, even as they recognised there was more to do to address their complicated histories, she said.

"We can hold our governments accountable through their democratic processes. And we can hold ourselves accountable for creating a more just and honest world," Ms Kennedy said.

Ms Kennedy thanked descendants of the Eureka Stockade for bringing Joseph's story to their attention and the embassy staff who worked with the cemetery trust see the plaque installed.