Both admired and feared by the populace, the Janissaries were the Sultan's elite soldiers - expertly trained warriors loyal only to their leader. Raised from early childhood through the devshirme system - the practice of conscripting intellectually and physically exceptional Christian children for permanent positions in Ottoman military and government - the Janissaries were a uniquely influential social class all their own. While they were not "free" in the standard sense, they nevertheless had an inordinate influence on Imperial politics, and any man who failed to gain their favor would never become an effective ruler.
As one historian of the era wrote: "(The Janissaries) terrified the people of Istanbul. 'Above all, don't let any of your people get into quarrels with the Janissaries,' the Porte functionaries advised foreign ambassadors, 'because we would be quite unable to do anything for you or for them.' When bands of Janissaries entered a district, the shopkeepers immediately shut up shop. It was usually impossible to stop them ransacking a city after it had surrendered...."
By the end of Mehmet II's reign, the Janissaries had become a military and political force with unprecedented power, and would begin to influence the course of the Empire's growth in ways no Sultan had ever dreamed.