According to Tacitus, the Aesti had the same customs and attire as the Germanic Suevi. It has been suggested that the Aesti worshipped the mother ofthe gods, similar to the Nerthus cult among northern Germanic peoples. Tacitus wrote that the Aesti were "the only people who collect amber—glaesum is their own word for it—in the shallows or even on the beach". Glaesum, an apparently Latinised word for amber, is the only surviving example of the Aestian language; it resembles the later Latvian equivalent: glīsis or glēsa. The word is possibly of Germanic origin, given its similarity to the Gothic word glas. Tacitus, however, describes their language as closer to that spoken in Britain than that spoken by other neighbouring tribes. The Old Prussian and modern Lithuanian names for the Vistula Lagoon, Aīstinmari and Aistmarės, respectively, appear to derive from Aesti and mari, which suggests that the area around the lagoon had links with the Aesti. Despite the phonological similarity between Aestii and the modern ethnonyms of Estonia, especially in popular etymologies, the two geographical areas are not contiguous and there are few, if any, direct historical links between them. The etymologies of Aesti and Eesti remain subjects of scholarly conjecture.
Historical sources
Tacitus
The ancient writers, beginning with Tacitus, who was the first Roman author to mention them in his Germania, provide very little information on the Aestii. Although Tacitus never travelled to Magna Germania himself and only recorded information he had obtained from others, the short ethnographic excursus below is the most detailed ancient account of the Aestii that we have: The placement of the Tacitean Aestii is based primarily on their association with amber, a popular luxury item during the life of Tacitus, with known sources at the southeastern coast of the Baltic Sea. The Baltic amber trade, which appears to have extended to the Mediterranean Sea, has been traced by archaeologists back to the Nordic Bronze Age; its major center was in the region of Sambia. This trade probably existed before the historical Trojan War in the 13th century BCE, as amber is one of the substances in which the palace of Menelaus at Sparta was said to be rich in Homer's The Iliad.
Cassiodorus
' Variae, published in 537, contains a letter written by Cassiodorus in the name of Theodoric the Great, addressed to the Aesti: The style of the letter proves that the nation was at that time independent, not ruled by the Ostrogoths. Apparently Cassiodorus considered it politically essential to establish friendly relations with the Nordic region. The letter also indicates that the Aesti were fully confident of the value of amber and had made out of it a trade secret. The sending of presents and the promise to show future favors were in ancient times a cordial way of giving de jure recognition to another power.
Sixth Century historian Jordanes makes two references to the Aesti in his book "The Origins and the Deeds of the Goths", which was a treatment of Cassiodorus' longer book on the history of the Goths. The first quote places the Aestii beyond the Vidivarii, on the shore of the Baltic: "a subject race, likewise hold the shore of Ocean." The next quote concerns the subjugation of the Aesti by Hermanaric, king of the Gothic Greuthungi: "This ruler also subdued by his wisdom and might the race of the Aesti, who dwell on the farthest shore of the German Ocean".
Alfred the Great
In an 11th-century manuscript of King Alfred's account of the voyage from Hedeby to Truso by Wulfstan, held by the British Museum, includes ethnographic information on the medieval Aestii, in which the terms Esti, Est-mere and Eastland are used referring to Old Prussians. In the text, a summary description of the country and its riches is followed by a very detailed account of the people's funeral customs. It mentions the old trading port Truso of Old Prussians and also calls the land a Witland - "the Vistula is a very large river, and near it lie Witland and Weonodland ; and Witland belongs to the Esthonians."
