As the sun set in Las Vegas on Sunday, tens of thousands of runners hit the road to take part in the city's annual marathon.
It was the biggest event since a gunman, hiding in a hotel room above the famous Strip, killed 58 people at an outdoor concert.
More than one month later, authorities still don't know what drove 64-year-old wealthy retiree Stephen Paddock to stage the attack. Paddock was found dead in his hotel room -- apparently from a self-inflicted gunshot.
The shadow of the October 1 mass shooting -- the deadliest in modern US history -- colored the mood at Sunday's event.
"There's a subdued tone to the race this year," marathon spokesman Dan Cruz told CNN affiliate KSNV.
Police had 350 officers on the ground and used dump trucks, buses and other large vehicles as barriers to protect the crowds, Las Vegas Metropolitan Police Captain Andy Walsh told CNN affiliate KTNV.
There were also counter-sniper surveillance posts along the route and coverage from the police department's helicopter unit, Walsh said.
The city also worked to install 800 steel posts along the Strip as part of larger plan to keep pedestrians and vehicles apart, KSNV reported.
The Rock 'n' Roll Marathon began at 4:30 p.m. local time (7:30 p.m. ET) and was expected to draw 40,000 runners from more than 70 countries, CNN affiliate KLAS reported.
Organizers billed it as "a unique opportunity for marathoners," saying the race starts at sunset, when "the city comes to life with lights shining like you've never seen before."
Few runners canceled their registrations in wake of last month's shooting, Cruz told KSNV.
Participants were warned to expect a greater security presence than in years past. Runners were funneled into a blocked-off starting area, where their bibs were checked and confirmed both upon entry and at the starting line.
Some say the shooting has given the marathon new meaning.
Esther Reincke told KTNV that she dedicated her marathon to Cameron Robinson, her coworker and running buddy who was killed in the shooting.
"I can run now and Cameron can't. That's really moving for me, to have somebody that was so young and so full of life and really just getting his life going," Reincke said.
Runners were encouraged to wear #VegasStrong t-shirts, and organizers included tributes to the victims along the race course. The first two and half miles were "an extended moment of silence," according to Cruz. The rest of the course followed the typical "Rock 'n' Roll Marathon formula" by featuring a live band at every mile to fire up racers.
The course also included a 300-foot #VegasStrong wall signed by runners and lit up in honor of the shooting victims.