The colours of the Belarusian flag were projected into the sky over the Latvian capital in a show of support for the Belarus opposition movement.
Riga was just one of many cities heeding a call to make February 7 Belarus Solidarity Day.
The request came from Svyatlana Tsikhanouskaya, the leader of the opposition movement who has been in exile in Lithuania since after the disputed election result in August that saw strongman Alyaksandr Lukashenka returned to power.
"People will go out to protest on the day of All-Belarus People's Assembly (that will discuss prospects for the country's development) because they already gather weekly in courtyards and districts despite detentions and repression," Tsikhanouskaya said in a video. "They are far more than the 2,700 delegates who attempt to replace the voice of the people."
She recommended holding rallies, posting support on social media, writing letters to political prisoners, and lighting the facades of buildings in red and white -- the colors of the Belarus opposition movement.
Tsikhanouskaya also invited people to join an online solidarity conference on February 6, which included discussions on Belarus and the launch of the Belarusian People's Embassies.
Czech Foreign Minister Tomas Petricek, who participated in the conference, told RFE/RL's Belarus Service that the ministry would express its concern "about the repression that we still see in Belarus" to mark the Day of Solidarity.
German Chancellor Angela Merkel, in her weekly podcast on February 6, said she had been "deeply impressed" by Belarus's democracy movement.
"The calculation by those in power seemed to be that the world would forget these brave people. We cannot let that happen," said Merkel, adding that the Belarusian government needed to put an end to violence against peaceful demonstrators.
Lukashenka's declaration of victory in August's presidential election was hotly disputed and has sparked continuous protests that have seen tens of thousands take to the streets demanding he step down.
He's run the country since 1994 but he denies any wrongdoing and refuses to negotiate with the opposition on resigning or holding new elections.
The European Union, United States, Canada, and other countries have refused to recognise Lukashenka as the legitimate leader of Belarus