Simon Busuttil, the country’s opposition leader, also posted on Twitter, saying, “This is a sad day for #Malta. We have just lost an icon of our country’s natural beauty.”

Malta, in the central Mediterranean, has a population of roughly 400,000 and counts tourism as a main economic driver. In recent years, rising interest in the arch and nearby sites has been driven in part by their appearance in the series “Game of Thrones,” which will air its seventh season on HBO this year. The Azure Window was a backdrop for the wedding of Daenerys Targaryen, a recurring character played by Emilia Clarke, to Khal Drogo, portrayed by Jason Momoa, in the first episode in mid-2011.

In 2013 a geological study of the site found that erosion was inevitable. Last year in response to that and to concerns for public safety, the authorities banned walking across the site, with a fine of just over $1,500 for lawbreakers.

In the end, nature — in the form of a heavy storm — not humans doomed the arch.

Roger Chessell, a local resident, told The Times of Malta he was at the site when it collapsed on Wednesday morning.