score:2
I am imagining the picture is stylized and not drawn to scale.
Depending on how close the shield on the ramp was placed to the gates of the city, the shield would do two things:
The defenders may have been able to fire flaming arrows at the shield in the hope of trying to destroy it by burning. This would require the shield to be within range, the archers to have the presence of mind to shoot flaming arrows.
As to the defense of the shield against such fire attacks: