Washington (CNN) Now we know what Justice Ruth Bader Ginsburg was doing while recuperating from cancer surgery and fielding calls about the Oscar-nominated documentary based on her life story.

She was delving deeply into the history of the excessive fines clause of the Constitution.

On Wednesday, her second day back on the bench, she read -- in her usual steady voice -- an opinion holding that the Eighth Amendment's ban on excessive fines applies to states and local governments, as well as to the federal government.

In her opinion, she traipsed through history: the Magna Carta, the 17th-century Stuart kings, the Virginia Declaration of Rights and the 14th Amendment.

"For good reason, the protection against excessive fines has been a constant shield throughout Anglo-American history: Exorbitant tolls undermine other constitutional liberties," she wrote.

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