BERLIN – Before an enormous crowd, Democratic presidential contender Barack Obama on Thursday summoned Europeans and Americans together to “defeat terror and dry up the well of extremism that supports it” as surely as they conquered communism a generation ago.

“The walls between old allies on either side of the Atlantic cannot stand,” Obama said, speaking not far from where the Berlin Wall once divided the city.

Associated Press U.S. Democratic presidential candidate Sen. Barack Obama, D-Ill. waves to the audience after a speech at the victory column in Berlin. Video A massive crowd gathered to hear Democratic presidential candidate Barack Obama speak in Berlin, Germany. Obama's speech was the centerpiece of a fast-paced tour through Europe designed to reassure skeptical voters back home. Media Player The FREE Windows Media Player is necessary to play Windows Media.

“The walls between the countries with the most and those with the least cannot stand. The walls between races and tribes, natives and immigrants, Christian and Muslim and Jew cannot stand,” he said.

Obama said he was speaking as a citizen, not as a president, but the evening was awash in politics. His remarks inevitably invited comparison to historic speeches in the same city by Presidents John F. Kennedy and Ronald Reagan, and he borrowed rhetoric from his own appeals to campaign audiences in the likes of Berlin, N.H., when he addressed a crowd in one of the great cities of Europe.

“People of Berlin, people of the world, this is our moment. This is our time,” he said.

Obama's speech was the centerpiece of a fast-paced tour through Europe designed to reassure skeptical voters back home about his ability to lead the country and take a frayed cross-Atlantic alliance in a new direction after eight years of the Bush administration.

Republicans, chafing at the media attention Obama's campaign-season trip has drawn, sought to stoke doubts abut his claims.

In Die Welt, the German publication, Rep. Thaddeus McCotter, R-Mich., said: “No one knows which Obama will show. Will it be the ideological, left-wing Democratic primary candidate who vowed to 'end' the war rather than win it, or the Democratic nominee who dismisses the progressing coalition victory as a 'distraction'? Will it be the American populist who has told supporters in the United States that he will demand more from our allies in Europe and get it, or the liberal internationalist hell-bent on being liked in Europe's salons?”

Obama met earlier in the day with German Chancellor Angela Merkel for a discussion that ranged across the wars in Iraq and Afghanistan, climate change, energy issues and more.

Knots of bystanders waited along Obama's motorcade route for him to pass. One man yelled out in English, “Yes, we can,” the senator's campaign refrain, when he emerged from his car to enter his hotel.

Obama drew loud applause as he strode confidently across a large podium erected at the base of the Victory Column in Tiergarten Park in the heart of Berlin.