Thousands of people in Washington have been commemorating the 40th anniversary of the "I have a dream" speech made by the civil rights leader, Martin Luther King. On 28 August 1963 he stood on the steps of the Lincoln Memorial and delivered his speech to a crowd of 250,000 people. It was the high point of the struggle for black equality in America and the demonstrators had marched on the US capital to call for jobs and freedom. Forty years on, the civil rights leader's son, Martin Luther King III, said that although there had been many achievements in the past four decades, there was still a long way to go.