Please answer a question about the following article about Greece:

In 1814, a secret organization called the Filiki Eteria (Society of Friends) was founded with the aim of liberating Greece. The Filiki Eteria planned to launch revolution in the Peloponnese, the Danubian Principalities and Constantinople. The first of these revolts began on 6 March 1821 in the Danubian Principalities under the leadership of Alexandros Ypsilantis, but it was soon put down by the Ottomans. The events in the north spurred the Greeks of the Peloponnese into action and on 17 March 1821 the Maniots declared war on the Ottomans.

The first of several revolutions began when?
6 March 1821