A 54-year-old letter Martin Luther King, Jr. wrote to civil rights heroine Rosa Parks is up for auction.

The note King wrote in April, 1960 went on sale on Tuesday (25Mar14) on website MomentsInTime.com for $125,000 (£78,000).

It is believed to be the only letter King wrote to Parks. In it, he responds to a letter he received from her in March, 1960.

It reads in part: "In the midst of constant harassment and intimidation because of my involvement in the civil rights struggle I often find myself asking, 'Is it worth it?' But then a friend of good will come along with kind and encouraging words that gives me renewed vigor and courage to carry on. Your letter serves such a purpose."

Parks became a civil rights figure in 1955 when she was arrested for refusing to give up her seat on a city bus to a white passenger in Montgomery, Alabama.