Baltia or Basilia is a legendary island in Roman mythology

Roman mythology

Roman mythology is the body of traditional stories pertaining to ancient Rome's legendary origins and religious system, as represented in the literature and visual arts of the Romans...

, said to be in northern Europe.

Sources

Pliny the Elder

Pliny the Elder

Gaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...

 (Nat. 4.27; 37.11):
Diodorus Siculus

Diodorus Siculus

Diodorus Siculus was a Greek historian who flourished between 60 and 30 BC. According to Diodorus' own work, he was born at Agyrium in Sicily . With one exception, antiquity affords no further information about Diodorus' life and doings beyond what is to be found in his own work, Bibliotheca...

 (v. 23):
Pliny quotes from the testimony of Xenophon of Lampsacus and Pytheas, as well as Timaeus, yet the writings from these individuals themselves on Baltia were lost, and Pliny only paraphrases. According to Pliny, Pytheas called Baltia "Basilia" and Timaeus the "Isle of Abalus". The Island is described as being to the far north and linked to amber.

Location Hypotheses

William Smith in his Dictionary of Greek and Roman Geography

Dictionary of Greek and Roman Geography

The Dictionary of Greek and Roman Geography, first published in 1854, was the last of a series of classical dictionaries edited by the English scholar William Smith , which included as sister works A Dictionary of Greek and Roman Antiquities and the Dictionary of Greek and Roman Biography and...

 (1854) wrote Baltia was "probably a portion of the Prussian coast upon the Baltic".

Alexander von Humboldt

Alexander von Humboldt

Friedrich Wilhelm Heinrich Alexander Freiherr von Humboldt was a German naturalist and explorer, and the younger brother of the Prussian minister, philosopher and linguist Wilhelm von Humboldt...

 placed Baltia west of the Jutland Peninsula

Jutland Peninsula

The Jutland Peninsula or more historically the Cimbrian Peninsula is a peninsula in Europe, divided between Denmark and Germany. The names are derived from the Jutes and the Cimbri....

 in the North Sea

North Sea

In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...

.