SAN JUAN, Puerto Rico — Clapping and raising their hands to the sky, hundreds of people clad in white gathered at an 18th-century fort in the Puerto Rican capital on Thursday to remember the thousands who died in the aftermath of Hurricane Maria as the U.S. territory struggles to recover one year after the Category 4 storm hit.

Religious leaders and government officials recalled how Puerto Rico was ravaged by the storm that killed an estimated 2,975 people and caused more than an estimated $100 billion in damage.

Tens of thousands remain without adequate shelter or reliable electrical power, a sad fact that Gov. Ricardo Rossello noted on Thursday.

“After that catastrophic experience, we acknowledge how complex and difficult it is to prepare for a hurricane of that magnitude and fury,” Rosello said. “The best tribute we can give these people, these brothers that we’ve lost, is to build a better Puerto Rico for their sons, their grandsons and their families.”

While the U.S. government has invested billions of dollars to help clean up and repair the U.S. territory, much work remains. Major power outages are still being reported, tens of thousands of insurance claims are still pending and nearly 60,000 homes still have temporary roofs unable to withstand a Category 1 hurricane.

“I think it’s inexplicable,” Kumi Naidoo, Amnesty International’s secretary general, told The Associated Press during a visit to the island Thursday. “There’s no justifiable reason I can see for this gross level of negligence.”

Across the island, people marked the one-year anniversary with gatherings large and small, solemn and anger-tinged — and at times, even hopeful.

In San Juan, the crowd of worshippers gathered at the 230-year-old San Cristobal fort sang and prayed along with pastors and musicians on stage, with music echoing through the fort’s heavy walls as the sun slowly sank into the sea behind them.