Question: What is the name of the ancient people first described by a Roman historian in his treatise that is adjacent to Prussia?

 According to Tacitus, Aestui, the land of the Aesti, was located somewhere east of the "Suiones" (Swedes) and west of the "Sitones" (possibly the Kvens), on the Suebian (Baltic) Sea. The Aesti (also Aestii or Aests) were an ancient people first described by the Roman historian Tacitus in his treatise "Germania" (circa 98 CE).  This and other evidence suggests that "Aestui" was in or near the present-day Russian enclave of Kaliningrad Oblast (previously East Prussia). <SEP> The Battle of Saticula, 343 BC, was the second of three battles described by the Roman historian Livy (59 BC – AD 17), in Book Seven of his history of Rome, Ab Urbe Condita, as taking place in the first year of the First Samnite War.  According to Livy's extensive description, the Roman commander, the consul Aulus Cornelius Cossus was marching from Saticula (in southern Italy) when he was almost trapped by a Samnite army in a mountain pass.  His army was only saved because one of his military tribunes, Publius Decius Mus, led a small group of men to seize a hilltop, distracting the Samnites and allowing the consul to escape.  During the night Decius and his men were themselves able to escape.  The next day the reunited Romans attacked the Samnites and completely routed them.  Several other ancient authors also mention Decius' heroic acts.  Modern historians are however sceptical of the historical accuracy of Livy's account, and have in particular noted the similarities with how a military tribune is said to have saved Roman army in 258 BC during the First Punic War. <SEP>  The territory and inhabitants were described by Tacitus in Germania in AD 98, where Suebi, Goths and other Germanic people lived on both sides of the Vistula River, adjacent to Aesti (further east). Prussia (Old Prussian: "Prūsa", German: "Preußen" , Lithuanian: "Prūsija" , Polish: "Prusy" ) is a historical region stretching from Gdańsk Bay to the end of Curonian Spit on the southeastern coast of the Baltic Sea, and extending inland as far as Masuria.  About 800–900 years later the Aesti were named Old Prussians, who since AD 997 repeatedly successfully defended against take-over attempt by the newly created Duchy of the Polans.  The territory of the Old Prussians and neighboring Couronians and Livonians was unified politically in the 1230s as the Teutonic Order State.  Prussia was politically divided in the period 1466-1772, with western Prussia under protection of the crown of Poland-Lithuania and eastern Prussia a Polish fief until 1660.  The unity of both parts of Prussia remained preserved by retaining its borders, citizenship and authonomy until western and eastern Prussia were also politically re-united under the Kingdom of Prussia.  It is famous for many lakes, as well as forests and hills.  Since the military conquest by the Soviet Army in 1945 and the expulsion of the inhabitants it divided between northern Poland (most of the Warmian-Masurian Voivodeship), Russia's Kaliningrad exclave, and southwestern Lithuania (Klaipėda Region).  The former German state of Prussia (1701–1947) derived its name from the region. <SEP> The Yuezhi or Rouzhi (, ) were an ancient people first reported in Chinese histories as nomadic pastoralists living in an arid grassland area in the western part of the modern Chinese province of Gansu, during the 1st Millenium BC.  After a major defeat by the Xiongnu, during the 2nd century BC, the Yuezhi split into two groups: the Greater Yuezhi ("Dà Yuèzhī" 大月氏) and Lesser Yuezhi ("Xiǎo Yuèzhī" 小月氏).