On March 12, 1930, Indian independence leader Mohandas Gandhi begins a defiant march to the sea in protest of the British monopoly on salt, his boldest act of civil disobedience yet against British rule in India.

Britain’s Salt Acts prohibited Indians from collecting or selling salt, a staple in the Indian diet. Citizens were forced to buy the vital mineral from the British, who, in addition to exercising a monopoly over the manufacture and sale of salt, also exerted a heavy salt tax. Although India’s poor suffered most under the tax, Indians required salt. Defying the Salt Acts, Gandhi reasoned, would be an ingeniously simple way for many Indians to break a British law nonviolently. He declared resistance to British salt policies to be the unifying theme for his new campaign of satyagraha, or mass civil disobedience.

On March 12, Gandhi set out from Sabarmati with 78 followers on a 241-mile march to the coastal town of Dandi on the Arabian Sea. There, Gandhi and his supporters were to defy British policy by making salt from seawater. All along the way, Gandhi addressed large crowds, and with each passing day an increasing number of people joined the salt satyagraha. By the time they reached Dandi on April 5, Gandhi was at the head of a crowd of tens of thousands. Gandhi spoke and led prayers and early the next morning walked down to the sea to make salt.

He had planned to work the salt flats on the beach, encrusted with crystallized sea salt at every high tide, but the police had forestalled him by crushing the salt deposits into the mud. Nevertheless, Gandhi reached down and picked up a small lump of natural salt out of the mud–and British law had been defied. At Dandi, thousands more followed his lead, and in the coastal cities of Bombay and Karachi, Indian nationalists led crowds of citizens in making salt. Civil disobedience broke out all across India, soon involving millions of Indians, and British authorities arrested more than 60,000 people. Gandhi himself was arrested on May 5, but the satyagraha continued without him.

On May 21, the poet Sarojini Naidu led 2,500 marchers on the Dharasana Salt Works, some 150 miles north of Bombay. Several hundred British-led Indian policemen met them and viciously beat the peaceful demonstrators. The incident, recorded by American journalist Webb Miller, prompted an international outcry against British policy in India.

In January 1931, Gandhi was released from prison. He later met with Lord Irwin, the viceroy of India, and agreed to call off the satyagraha in exchange for an equal negotiating role at a London conference on India’s future. In August, Gandhi traveled to the conference as the sole representative of the nationalist Indian National Congress. The meeting was a disappointment, but British leaders had acknowledged him as a force they could not suppress or ignore.

India’s independence was finally granted in August 1947. Gandhi was assassinated by a Hindu extremist less than six months later.