For some, the sounds of sirens alone are enough to evoke the memories.<br/> <br />And the sight of smoke can choke the heart.<br/> <br />Thirteen years after al Qaeda attacked the United States, the pain remains.<br/> <br />In what has become an annual ritual, politicians, dignitaries and victims' relatives gathered in New York, at the Pentagon and in rural Pennsylvania.<br/> <br />From Gordon Aamoth Jr. to Igor Zukelman, victims' names were read in lower Manhattan where the World Trade Center's twin towers once stood.<br/> <br />During a private ceremony at the Pentagon, President Barack Obama said no attack could stop America.<br/> <br />(SOUNDBITE) (English) PRESIDENT BARACK OBAMA SAYING:<br/> <br />"Thirteen years after small, hateful minds conspired to break up, America stands tall and America stands proud. And guided by values that sustain us, we will only grow stronger."<br/> <br />The anniversary comes as the U.S. faces what Obama calls an increasing danger.<br/> <br />He announced Wednesday night an aerial bombing campai
