You gotta give the siege more than just firework. Make the flames a character in their own right—maybe a rogue torch‑smith who decides the city’s fate, or a councilman who’s secretly selling the gates to the enemy. Drop in a small side quest that happens while the walls are cracking—like a lost heir found in the rubble. Keep the pacing tight: let the main conflict build with a ticking clock, then let the sparks be the climax that pushes the story forward. If you treat the blaze like a plot device rather than a backdrop, the city will feel alive, not just a setpiece.