The high attendance was undoubtedly helped by blue skies and sunshine as well as the fact that this year May 9 falls on a Saturday.
Known as "Victory Day" to Russians, May 9 remains a divisive date in Latvia. While ethnic Russians, who make up around a quarter of the population, see it as a day of commemoration and celebration, many ethnic Latvians see it as the start of a harsh 50-year Soviet occupation.
The official Latvian day for commemoration of victory over the Third Reich is May 8.
Caught between Russia and Germany, more than 100,000 Latvians fought on each side during the war.
Police were reluctant to give estimates of numbers attending but LSM and other media estimated that the total number of attendees could be around 100,000 by the time the events reach a climax with a fireworks display.
Among those present to lay flowers and listen to music was Alfreds Rubiks, the former Latvian Communist Party chief who attempted to lead a counter-coup as Latvia struggled to regain its independence.
"This day marks the end of the war and the liberation of Latvia by Soviet soldiers," Rubiks told LSM.
He denied the Soviet Union had been an occupying power itself.
"I object to such attempts to rewrite history and rehabilitate fascism, he said.
The St George ribbon, which has become a symbol of support for Russia-backed rebels in Eastern Ukraine as well as for fallen Soviet soldiers, was worn by the majority of attendees.
By early evening, police told LSM five people had been cautioned, four for drink-related offences and one for threatening behaviour.
Riga Mayor Nils Usakovs gave a speech in which he recounted tales of Nazi atrocities that had been told to him by members of his family - and of the family members he had himself lost.
"Family memory is not dependent on the political situation, geopolitical or ideological propaganda," Usakovs said.
"And family memories, never under any circumstances, should be be dismissed. That is why we always celebrate 9 May as Victory Day."