In October 1899, Stalin began work as a meteorologist at the Tiflis observatory. He attracted a group of supporters through his classes in socialist theory and co-organised a secret workers' mass meeting for May Day 1900, at which he successfully encouraged many of the men to take strike action. By this point, the empire's secret police, the Okhrana, were aware of Stalin's activities in Tiflis' revolutionary milieu. They attempted to arrest him in March 1901, but he escaped and went into hiding, living off the donations of friends and sympathisers. Remaining underground, he helped plan a demonstration for May Day 1901, in which 3,000 marchers clashed with the authorities. He continued to evade arrest by using aliases and sleeping in different apartments. In November 1901, he was elected to the Tiflis Committee of the Russian Social Democratic Labour Party (RSDLP), a Marxist party founded in 1898.