The Baltic tribes did not maintain close cultural or political contacts with the Roman Empire, but they did maintain trade contacts (see Amber Road). Tacitus, in his study ''Germania'', described the Aesti people, inhabitants of the south-eastern Baltic Sea shores who were probably Balts, around the year 97 AD. The Western Balts differentiated and became known to outside chroniclers first. Ptolemy in the 2nd century AD knew of the Galindians and Yotvingians, and early medieval chroniclers mentioned Old Prussians, Curonians and Semigallians.