Early Christianity: The orb was originally a symbol of Roman imperial power (as in the globus held by emperors), signifying rule over the world.
After Christianization: The cross was added atop the orb, transforming a pagan imperial emblem into a Christian one.
Medieval and Renaissance Europe: The globus cruciger became a key element of royal regalia in both the Holy Roman Empire and later European monarchies. It appeared in coronation ceremonies, royal portraits, and on coats of arms.