Marchers in Washington, New York, Boston protest police killings

Protesters angry over police shootings of unarmed black men had vowed to march on Saturday in major cities across the U.S.

They made good on their promise ... with hundreds of thousands of demonstrators reportedly taking to the streets ...

... in Washington, Boston and New York ... as well as smaller protests across the Bay Area and elsewhere.

Organizers say the marches were among the largest in the recent wave of so-called Ferguson protests ...

... venues to vent frustration over the killings of black men by white officers in Ferguson, Missouri, New York and Cleveland.

In Boston, police said they arrested 23 people for disorderly conduct after protesters tried to block a highway.

In New York, demonstrators -- possibly as many as 30,000 of them -- marched along Manhattan's Fifth Avenue.

They sometimes taunted police along the march route and by nightfall they were stopping traffic at the Brooklyn Bridge.

The protests are putting the treat