Who was pytheas? What did he do

Pytheas was a Greek geographer and explorer from the Greek colony of Massalia (modern-day Marseille). He made a voyage to northwestern Europe in about 325 BC and traveled all the way around Great Britain. He wrote the first account of Scandinavia, but his description of it has not survived. He is often referred to as the first known explorer in the modern sense of the word. Pytheas was known to have visited the Arctic, polar ice, and the Germanic tribes, and is the first person on record to do so. The Greeks looked to break the monopoly and thus sought a reliable route to the tin mines. Pytheas successfully circumnavigated a considerable portion of Great Britain and described the land in his now-lost memoir. In this works, he also described another land called the "Island of Thule." Now often considered to be an island in antiquity, Thule was sometimes identified as Iceland or Greenland, giving rise to the belief that Pytheas might have reached as far as Iceland. As astute astronomer, he was among the first ones to have suggested that the tides are affected by the moon. He was the first known person to describe the Midnight Sun, and also the first person to associate the tides to the phases of the moon. He was possibly the only source of information on the North Sea and the subarctic regions of Western Europe to later periods. Pytheas, (flourished 300 bc, Massalia, Gaul), navigator, geographer, astronomer, and the first Greek to visit and describe the British Isles and the Atlantic coast of Europe. Though his principal work, On the Ocean, is lost, something is known of his ventures through the Greek historian Polybius