Humans had free will to ignore divine guidance and the behavior required by "maat", but by doing so they could bring divine punishment upon themselves. A deity carried out this punishment using its "ba", the force that manifested the god's power in the human world. Natural disasters and human ailments were seen as the work of angry divine "ba"s. Conversely, the gods could cure righteous people of illness or even extend their lifespans. Both these types of intervention were eventually represented by deities: Shed, who emerged in the New Kingdom to represent divine rescue from harm, and Petbe, an apotropaic god from the late eras of Egyptian history who was believed to avenge wrongdoing.