Pytheas of Massalia or (using the Latin form) Massilia (4th century BCE), is a Greek geographer and explorer from the Greek colony, Massalia (modern day Marseilles).
He makes a voyage of exploration to northwestern Europe at about 325 BCE.
He travels around and visits a considerable part of Great Britain.
Pytheas is the first person on record to describe the Midnight Sun, polar ice, Germanic and possibly Finnic tribes.
He introduces the idea of distant Thule to the geographic imagination.
His account of the tides is the earliest to state they are caused by the moon.