Passage: In Zemun, the crusaders became suspicious, seeing Walter's sixteen suits of armor hanging from the walls, and eventually a dispute over the price of a pair of shoes in the market led to a riot, which then turned into an all-out assault on the city by the crusaders, in which 4,000 Hungarians were killed. The crusaders then fled across the river Sava to Belgrade, but only after skirmishing with Belgrade troops. The residents of Belgrade fled, and the crusaders pillaged and burned the city. Then they marched for seven days, arriving at Niš on 3 July. There, the commander of Niš promised to provide escort for Peter's army to Constantinople as well as food, if he would leave right away. Peter obliged, and the next morning he set out. However, a few Germans got into a dispute with some locals along the road and set fire to a mill, which escalated out of Peter's control until Niš sent out its entire garrison against the crusaders. The crusaders were completely routed, losing about 10,000 (a quarter of their number), the remainder regrouping further on at Bela Palanka. When they reached Sofia on 12 July they met their Byzantine escort, which brought them safely the rest of the way to Constantinople by 1 August.

Question: Where did the commander say he would provide escort to?
Constantinople