Nearly six years ago, The Related Group developers won a bruising battle at Miami City Hall for approval of three high-rise condo towers next to Mercy Hospital on Biscayne Bay — only to see the zoning changes for the buildings overturned in a court challenge.

The plans for the controversial project were abandoned, the towers never built. But an unusual lawsuit over the deal lives on today.

On Thursday, a Miami-Dade jury began hearing testimony in a suit brought against the developers by The Vizcayans, a support group for the Vizcaya Museum and Gardens that led the legal fight against Related’s condo project.

The Vizcayans have accused The Related Group and other investors in the project of conspiracy, saying the developers used a coterie of lobbyists, lawyers and consultants to essentially rig the vote on the project, forcing The Vizcayans and other project opponents into a lengthy — and needless, they say — court dispute.

Now The Vizcayans want Related and its partners to pay the cost of their legal fees in fighting the project — as much as $1.3 million.

“The Vizcayans never reached out to pick a fight,” Stephen Darmody, an attorney for the group, said in opening statements. “If it had never been for the wrongful acts of the developers, The Vizcayans never would have been drawn into this litigation.”

Darmody said he had email records and other evidence showing how Related’s executives, including chairman Jorge Perez, worked behind the scenes to win approval from Miami city commissioners weeks before the official vote. The Vizcayans also plan to show how the developers used the promise of cash — as much as $8 million — to win the approval of nearby neighborhood groups.

John Shubin, a lawyer for the developers, said his clients merely followed the traditional political process for getting a project approved at city hall. The Vizcayans, he said, are relying on a novel legal claim to try to get around the traditional American rule that each party in a legal dispute must pay for their own legal fees.

“There is absolutely no evidence of a conspiracy,” Shubin told jurors. “They didn’t care about The Vizcayans. They were trying to get a project built. … You can’t have a claim for money damages for coming to government and asserting your rights.”

The Related Group’s condo proposal was ambitious and contentious: The developers wanted to build three towers (the tallest over 400 feet) on a 6.7-acre parking lot next to Mercy Hospital in Coconut Grove, just south of the Vizcaya grounds. A Canadian developer who teamed with Related on the deal paid $96 million to the hospital for the site.

Vizcaya’s administrators thought the looming towers would cast a shadow over the property, the city’s only national historic landmark. The museum’s trustees agreed to have The Vizcayans, who raise money for the museum, pursue a legal fight against the project.

By then, the developers had already begun to quietly drum up support for the plan, in part through “unlawful” behind-the-scenes meetings with city commissioners, The Vizcayans argued in court papers.

A Related vice president told colleagues in a December 2006 email that two commissioners at the time, Angel Gonzalez and Joe Sanchez, had already agreed to support the plan — three months before the commission vote on the zoning changes, Darmody told jurors.