Celebrations included a massive military parade in Moscow's Red Square, where Russian President Vladimir Putin hosted several foreign leaders, including the presidents of China and Brazil.
At the northern end of the Black Sea, Crimea sits at the crossroads of Europe and Asia, having been at various times in its long history either coveted, conquered or controlled by various powers.
Russia declared a three-day ceasefire in Ukraine starting May 8 for the anniversary of the Soviet Union's victory over Nazi Germany. Ukraine called for an immediate, 30-day truce instead.
It was their first face-to-face meeting since they argued in front of cameras in the Oval Office in February — and comes as efforts intensify to end Russia's war in Ukraine.
President Trump has put Steve Witkoff — a friend from New York's real estate world — in charge of delicate talks on the war in Ukraine, Iran's nuclear ambitions and the conflict in Gaza.
President Trump lashed out at Ukrainian President Volodymyr Zelenskyy again on social media, after the Ukrainian leader refused to accept Russia's 2014 annexation of Crimea.