BEIRUT, Lebanon — Little by little, the central Syrian city of Homs is losing its infrastructure and its landmarks. The national hospital lies in ruins. Rebel-held neighborhoods stretch for blocks without an intact building. Many government offices are closed. The silver-domed mosque of Khalid bin al-Waleed — named for an early Islamic warrior particularly revered by Sunnis — stands pockmarked and perforated.

Abandoned cars rust beneath piles of rubble and downed wires.

Homs was an early bellwether of what Syria would become. One of the first cities to rise up in rebellion, it was home to mass demonstrations. As protests turned to armed revolt, the city began to split, largely along sectarian lines, with much of the Sunni majority supporting the uprising and members of President Bashar al-Assad’s Alawite sect joining pro-government militias. Now, after more than a year of siege, bombardment and clashes, which have intensified recently as the government has renewed its assault on rebel strongholds, Homs may well be the site of the most concentrated destruction in the country.

“For two years, the regime couldn’t retake Homs,” said a man who identified himself as Abu Nizar, 55, a resident of the Ensha’at district. “Now they want to retake it, but after changing its demographic and sectarian fabric.”

For many months, Homs has been a city divided. Several central areas have been gradually flattened as they have changed hands, with the army briefly retaking control, only to lose it again. Government-held areas continued to function, with shops and restaurants open, preserving a rhythm of daily life. But recently, the government sought to break what amounted to a stalemate. The army began raining rockets and shells onto rebel areas in and around the old city center as pro-government fighters vowed to retake control and open a route to the north.