Długosiodło [dwuɡɔˈɕɔdwɔ] is a village in Wyszków County, Masovian Voivodeship, in east-central Poland. It is the seat of the gmina (administrative district) called Gmina Długosiodło. It lies approximately 21 kilometres (13 mi) north-east of Wyszków and 73 km (45 mi) north-east of Warsaw. Site of the battle between the Duchy of Masovia knights and the combined force representing warriors and knights of Duchy of Lithuania under prince Mendog (Mindaugas) or chief Treniota, Yotvingians, Ruthenians of Halych under prince Shvarno laden with booty and prisoners from their raid on Masovia (amongst other successes during their 1362 raid they took the capital of principality Płock and killed prince Siemowit I of Masovia and took his son Konrad II of Masovia prisoner when took the stronghold of Jazdów, today Ujazdów Warsaw).