Serbia; city of Sremska Mitrovica: Interior of roofed archeological site of Imperial Roman Palace of antique Sirmium (Serbian: Carska palata Sirmijuma); with mosaics; reception area (front; right); and heating system around atrium (back); background Roman city of Sirmium: Sirmium (city of Sremska Mitrovica; Serbia); background Sirmium: On crossroads from West to East and North to South and on the banks of Sava river (Latin: Savus); Roman Sirmium; conquered 13 - 9 BC; became one of the most important towns of Late roman Empire. In 103 AD; it became capitol of Roman province of Lower Pannonia. In 293 AD; when the Empire was split into four parts (tetrarchy) under emperor Diocletian; Sirmium became even capitol of the empire; along with today's Trier (Germany); Medilanum (today: Milan; Italy); and Nicomedia (Turkey) and "famous and populous mother of cities". Historians still doubt; weather Sirmium in 3rd and 4th century AD really reached a number of 100 000 inhabitants. Most probably; it arrived at present size of Sremska Mitrovica (41600 inhabitants). Emperor Trajan started his campaign against Dacians; here; and Emperor Galerius fist took seat here. Minimum 5 (others count 10) Roman Emperors were born in or around Sirmium: Trajan Decius; Aurelian; Probus; who invented viniculture in the surroundings; Maximinianus Herculius and Gratian. Further emperors resided here: Domitian; Marcus Aurelius (from 170 - 180); who probably died here; Septimius Severus; Maximinus Thrax; Claudius II Gothicus; Diocletian and usurpers Ingenuus and Regalian. Under Diocletian; Licinius; Constantine the Great; Constantius II; Julian; Valentinian I; Gratian and even Theodosius seat of government was placed in this prosperous city. And there is the Christian Sirmium; place of the two synods (357 - 359 AD); with its first bishop Irenaeus; who was decapitated on Roman Sava Bridge; in 304 AD. 1957; excavations were started at Sirmium Imperial Palace; a basilica; which was discovered by chance du