Police detained anticorruption activist Aleksei Navalny (pictured) as thousands rallied, and dozens were arrested, in cities across Russia in some of the larger public demonstrations the country has seen in years.

Navalny, a gadfly crusader whose fight against graft has resonated with many Russians, was detained as he emerged with supporters from a subway station March 26 in central Moscow.

On Twitter, Roman Rubanov, the director of Navalny’s nongovernmental foundation, posted videos of a crowd of supporters trying to prevent the van carrying Navalny from moving amid a heavy riot police presence.