Attending World War II veterans, many of which are over 90 years old, also had to quarantine for two weeks so that they could sit with President Vladimir Putin at the ceremony.
"It was a awful and massive tragedy that claimed millions of lives, leaving behind devastation and irreparable pain of loss, deep never-healing wounds", Putin said, addressing soldiers outside the cathedral.
Putin attends the Victory Day Parade, which had been delayed due to the coronavirus, in Red Square in Moscow on Wednesday.
The reforms, the first major changes to Russia's basic law since 1993, will reset presidential term limits, potentially allowing Putin to serve two more terms.
He announced the new dates for the parade and the vote - initially planned for April - last month despite Russian Federation still recording thousands of new coronavirus cases every day. Asked if Russian Federation could build more trust between India and China, Lavrov said Moscow had never made such an attempt because both countries "have everything they need".
This year, 14,000 troops and several hundred military machines took part in the parade, including 30 historic T-34 tanks.
Pictures showed that social distancing being maintained at the Red Square where the parade will take place.
Ahead of the parade, he slammed the West for "insulting Russia" by playing down the USSR's role in winning the war.
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He said: "I think Chelsea are sitting a little bit nervously". "We got rid of the heavy backpack". "I've never thought, 'Always we can win, '" he said.
Opening a military cathedral on Monday, Putin said the Soviet wartime victory remained a touchstone for modern Russian Federation, calling it a sacred memory.
Russian Federation has recorded over 600,000 virus cases, the third largest epidemic in the world, behind only Brazil and the United States.
The Kremlin has also included a number of other proposed amendments for Russians to vote on, created to have conservative and nationalist appeal.
The Russian leader said last week he had not decided whether to seek another term after 2024, but that it was essential he have the option of extending his term.
The Russian head of state argued that, instead of deliberating where exactly COVID-19 "came from", countries should now focus on dealing with the current threat posed by the pathogen.
Moscow Mayor Sergei Sobyanin described the reforms as necessary if the country wanted to "guarantee stability, remove uncertainty".
Seventy-five Armenian servicemen marched along the Red Square. Though the new date of voting was fixed for July 1, officials have announced that polling would begin a week early to prevent overcrowding at the polling stations.
It was a "triumph of unprecedented power", Putin said in his speech.
Opposition politician Alexei Navalny has previously condemned the vote as a populist ploy created to give Putin the right to be "president for life", calling it a "violation of the constitution, a coup".