Fire crews fought a blaze which threatened to destroy Lancaster's St Nicholas Arcades tonight.
A Lancashire Fire and Rescue spokesman said if they hadn't got there so quickly, the blaze could have wrecked the arcade.
Seven engines fought the fire which fire crews believe was started deliberately. Crews were called to the roof of the Poundland store at Lancaster Gate at around 8.50pm tonight (Wednesday June 1).
Flames could be seen coming from behind the Wilko store and spreading into Penny Street, Market Street and the city centre.
Lancaster Fire Crew Manager Scott Lee said: "We believe it was deliberate, some people got up on the roof, we don't know how, spilt some oil of some sort and set it on fire.
"When we arrived town was pretty quiet, we got up onto the roof through Diggle's, luckily the lady was still there and it took us about 30 minutes to extinguish the fire."
There were no casualties and an investigation is underway.