WATCH: Elon Musk speaks at Donald Trump's post-inauguration celebration at Capital One Arena

Billionaire Elon Musk gave what appeared to be a fascist salute during his speech at a post-inauguration celebration for President Donald Trump on Monday at the Capital One Arena, where he also promised safe cities and that the U.S. would land astronauts on Mars. “Some elections are important, some are not. But this one, this one really mattered and I just want to say thank you for making it happen,” Musk said before putting his hand on his chest and then raising it in a salute that appeared similar to the “Sieg Heil” used by Nazis at their victory rallies. “It is thanks to you that the future of civilization is assured," Musk said. Trump named Musk and entrepreneur Vivek Ramaswamy to lead the "Department of Government Efficiency," an outside commission aimed at identifying federal programs and spending to cut. After Trump was sworn in, multiple lawsuits were filed against the Trump administration claiming that the move violates federal transparency laws. Musk said that because of Trump's election, the U.S. would have “safe cities, secure borders, sensible spending, basic stuff” and the United States would land astronauts on Mars. “Can you imagine how awesome it will be to have American astronauts plant the flag on another planet for the first time?" he asked the crowd. The inauguration ceremony, including the swearings-in, is taking place indoors this year, a last-minute change to the pomp and circumstance due to extreme cold forecasted for the nation’s capital. Thousands of guests gathered for an indoor celebration and parade in Capital One Arena. Watch PBS News for daily, breaking and live news, plus special coverage. We are home to PBS News Hour, ranked the most credible and objective TV news show. Subscribe for exclusive content in our newsletters: https://www.pbs.org/newshour/subscribe PBS News podcasts: https://www.pbs.org/newshour/podcasts Stream your PBS favorites with the PBS app: https://to.pbs.org/2Jb8twG Find more from PBS News at https://www.pbs.org/newshour Subscribe to our YouTube channel: https://bit.ly/2HfsCD6 Follow us: TikTok: https://www.tiktok.com/@pbsnews X: http://www.twitter.com/newshour Instagram: http://www.instagram.com/newshour Facebook: http://www.pbs.org/newshour