Arsonists are believed to have set fire to tyres and wood pallets on the A10.
One crew from Ely was called to the fire in the open near Chettisham at 10.53pm on Saturday May 11.
Firefighters arrived to find tyres and wood pallets on fire.
The crew extinguished the fire and returned to their station by 12.25am.
The cause of the fire is believed to be deliberate.
Anyone with information should contact police by visiting www.cambs.police.uk to submit an online report or call Crimestoppers on 0800 555111.
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