Sürsat was a form of food requisitioning with price controls, used by the Ottoman Empire to provide consumables for its armed forces.
[1] It was related to nüzül; sürsat was initially an obligation for the public to provide food and other supplies at a pre-fixed price which was unlikely to be favourable, or might even be merely symbolic.
Over time, nüzül, sürsat, and istira were all transformed into extraordinary cash taxes on people living near the route travelled by the army.
[1][2] During the late 17th and early 18th century - a period of continuous warfare for the Ottoman Empire - these extraordinary taxes soon became routine.
The easy convertibility of food supply obligations to cash payments makes it clear that sürsat was effectively a tax.