With his hand on a Bible once owned by John Quincy Adams, Deval Patrick was sworn in Thursday as Massachusetts' 71st governor and only the second black elected governor in U.S. history.

The ceremony on the Statehouse steps was the culmination of a longshot political campaign to replace Republican Mitt Romney, who is considering a 2008 bid for president.

"We meet today on a singular occasion, more than the passing of title and honor, more than the ritual transfer of the power of government," Patrick, 50, told a crowd of thousands that stretched into Boston Common.

"This is the occasion when the people charge new leadership to steward the public trust. It is a profound responsibility and I accept it humbly," he said.

In the crowd before him were thousands of supporters who had helped propel the Democrat to victory in his first attempt at elective office.

L. Douglas Wilder, who became the nation's first black elected governor in 1990 in Virginia, was among them. Also sitting in chairs at the base of the Statehouse steps were four former Massachusetts governors: Democrat Michael S. Dukakis and Republicans William F. Weld, Paul Cellucci and Jane M. Swift.

Romney, who had decided not to seek a second term and filed papers Wednesday to form a presidential exploratory committee, stayed home during the ceremony Thursday before heading into his new headquarters to work on his campaign.

Patrick grew up poor on Chicago's South Side, attended Harvard and its law school, then worked as a civil rights lawyer for the poor and then in a corporate law firm in Boston.

During the Clinton administration, he led the Justice Department's civil rights division.

He also was appointed chairman of Texaco Inc.'s Equality and Fairness Task Force, following the settlement of a race discrimination case at the company in 1997 and became vice president and general counsel for Texaco Inc. in 1999. He served as executive vice president and general counsel for The Coca-Cola Co. from 2001 to 2004.

Patrick's inauguration ended a 16-year run of Republican rule in Massachusetts that began in 1991, when Weld replaced Dukakis.

The Bible Patrick placed his hand as he repeated the oath Thursday had been given to Adams, the nation's sixth president, by slaves from the ship Amistad whom Adams had helped to free.

"I am descended from people once forbidden their most basic and fundamental freedoms, a people desperate for hope and willing to fight for it — and so are you," Patrick told the crowd. "This commonwealth, and nation modeled on it, is at its best when we show that we understand a faith in what's possible and willingness to work for it.

"As an American, I am an optimist, but not a foolish one. I see clearly the challenges before us."