Congress certified Friday what the world has known for nearly two months -- President Barack Obama's re-election, which was made official through the counting of the Electoral College's votes.

Only then, after votes from each of the 50 states and the District of Columbia were tabulated, was Obama officially declared the winner over Republican Mitt Romney -- a quaint formality, perhaps, but also constitutionally required.

A relic of when Americans traveled on horseback and interstate communication was less than instantaneous, electoral law provides for long delays between the popular vote and the announcement of a result by a joint session of Congress.

In reality, the outcome was known on election night on November 6, but the US president is not directly elected by the popular vote -- at least not technically.

Instead, Americans in each of the 50 states, as well as the capital, cast their ballots to elect 538 electors: 332 representing Obama and 206 for Romney.

Vice President Joe Biden, who serves as president of the US Senate, presided over Friday's joint session of Congress, when legislators read out the tallies from each state.

"This announcement of the state of the vote by the president of the Senate shall be deemed a sufficient declaration of the persons elected president and vice president of the United States," Biden declared.

The count is steeped in American electoral tradition, one which sees the votes carried in a box from the Senate through the Capitol Rotunda to the House of Representatives, in a procession including Biden and the congressional leadership.

The total figure of electors, and how many are assigned from each state, depends on the population.

On December 17 -- the first Monday after the second Wednesday in December -- these delegates cast their votes in each US state.

Only around half the states require the electors to vote for the candidate they represent, but it is extremely rare for an elector to change candidates or abstain.

The last time there was a "faithless elector" was the year 2000, when District of Columbia Democrat Barbara Lett-Simmons abstained from voting for her party's candidate Al Gore, for whom she was expected to cast her vote, as a protest of the capital city's lack of voting representation in Congress.

Her abstention did not affect the election's outcome.

In the hypothetical situation where no candidate obtained a majority, the House of Representatives would be responsible for choosing a winner, with one vote per state delegation.

Meanwhile, plans were well underway for Obama's second inauguration: a private swearing in on January 20, followed by an immense public ceremony the following day.