The Macestus Bridge or Bridge of Sultançayır was a Roman segmental arched bridge across the Macestus River (Turkish: Simav or Susurluk Çayı) at Balıkesir, in the northwestern part of modern-day Turkey. Its flattened arches, slender piers and the hollow chamber system documented the progress made in late antique bridge building. A first cursory investigation of the 234 m long structure was conducted in the early 20th century, but since then its existence has been largely neglected by scholars. Current photos from 2009 show that the bridge has collapsed in the meantime.