STEVEN Spielberg's film Lincoln is not for any cinemagoer seeking easy entertainment.

It is serious, grimly realistic and more or less historically accurate. Daniel Day-Lewis gives an outstanding performance as Abraham Lincoln, portraying him with his human complexities; gentle, wise and utterly resolute.

The film focuses on the last four months of Lincoln's life (from January to April 1865) and concentrates on his struggle to get through Congress the 13th Amendment to the Constitution, the abolition of slavery. In doing so it expands an area that has offered limited information to researchers and has been given much less space in biographies than his far more visible action in issuing the Emancipation Proclamation two years earlier.

The Proclamation is a precisely worded document which legions of historians have pored over and examined minutely, as they have done with his speeches and letters. For the passage of the 13th Amendment, sparse evidence is available. Lincoln used his influence behind the scenes.

He is famous for his Proclamation declaring slaves in rebel-held localities were free, but he knew it was only a document issued in time of war "upon military necessity", was of doubtful legality and could be quashed by a future President. What was needed was a Constitutional Amendment to complete his task and he was determined to achieve this.

The 13th Amendment, sponsored by the Republicans, came before the House of Representatives on January 31, 1865, and both sides knew the outcome would be close. The Democrats were going to vote against it, and Lincoln and his emissaries worked to induce particular members to change their minds.

How they did this is uncertain, although a few stories have been aired. The film shows much lobbying going on, and it appears to be based on the reminiscences of individuals published years later of what allegedly was said to them.

Lincoln talked with some Democrats. David Herbert Donald, in his 1995 biography, says if Lincoln used other means of persuading Congressmen to vote for the Amendment, his actions were not recorded, and conclusions about the President's role rested on gossip. Stephen B Oates wrote in 1984 that there were "secret negotiations never made public".

In the event, the 13th Amendment was carried by 119 votes to 56, reaching the required two-thirds majority by only three votes. Doris Kearns Goodwin, in her book Team of Rivals, says that without five Democrats who had changed their votes the Amendment would have been lost.

Lincoln hailed the successful measure to end slavery as "a King's cure for all the evils". What is surely the greatest reform in American history was hard won.

It is known that during his presidency, Lincoln employed the patronage of his great office. On screen, he is seen buttonholing individuals and requesting their support. The saint-like folk hero of myth was really a politician of exceptional shrewdness and subtlety.

Christopher Reekie,

12 Orchard Drive,

Edinburgh.