If we build one bridge, we can have an Euler path. Two bridges must be built for an Euler circuit.

Three dots aligned in a vertical column left of a single dot on the right. Lines connect the dot on the right to each dot on the left. Among the dots on the left, two arced lines connect the bottom dot to the center dot, and two more connect the center dot to the top dot. An additional dashed edge connects the right dot to the top dot and another dashed edge connects the bottom dot to the middle dot in the vertical column.