U.S. President Joe Biden made a surprise stop in Kyiv Monday, ahead of a scheduled trip to Poland four days before the first anniversary of Russia’s full-scale invasion of Ukraine.

Against the wishes of the secret service and the Pentagon, Biden arrived in the besieged capital following a covert operation to conceal his whereabouts, which involved a 10-hour train ride from the Polish border. Many gathered in Heaven’s Hundred Square, which was barricaded and surrounded by military and police officials, to spot Biden.