Greek Colonisation is something of misnomer on two counts. First of all is the fact that there was no unified Greek state until the time of Alexander the Great. Instead the territory was fragmented into a number of competing city- states (poleis) that formed shifting alliances to meet the exigencies of the day.
Secondly, the term ‘colonisation’ did not mean the same then as it does today. Individual city states had their own expansion ambitions, which were generally concerned with trade rather than territory. It seems that most of the colonies began as trading posts, known as emporia(a) , some developing into towns, others grew into urban centres and even established colonies of their own.
In the first millennium BC, some of the Greek city-states gradually expanded their influence(c) eastward into Asia Minor and the Black Sea and westward along the northern coast of the Mediterranean, eventually founding Massalia (modern Marseilles), which established emporia in eastern Spain.
The Phoenicians had their own city-states such a Tyre, Sidon and Byblos. They established ‘colonies along north Africa, and Spain. They competed with the Greeks, particularly in the central Mediterranean, where at one point they shared Sicily. Settlers from Tyre founded Carthage, which in turn became more powerful than and independent of its parent city and became more belligerent, eventually engaging in a series of wars with Rome, which it lost.
There is much more relevant information to be found on the excellent Ancient History Encyclopedia website(b) .
Pytheas was a 3rd century BC navigator from the Greek colony of Massalia (Marseilles) and is best known for his voyage in the north Atlantic, possibly around 240 BC. His trip took in the British Isles and as he ventured further north and claimed to have reached Thule. An assertion that has generated volumes of debate regarding Thule’s location. Pytheas described Thule as lying six day’s sail to the north of Britain. Iceland, Norway and the Faroes along with the Scottish Shetland and Orkney Islands have all been proposed as Thule.
Rhys Carpenter devoted an interesting chapter of his Beyond the Pillars of Hercules in which he suggested that Pytheas’ voyage was undertaken with commercial objectives in mind, but on that level it was unsuccessful. However, as a voyage of discovery, it was an unparalleled achievement earning for Pytheas Carpenter’s accolade of ”antiquity’s Greatest Explorer”.
Carpenter favours the idea that the term, ‘Pillars of Hercules’, when applied to the Strait of Gibraltar was used with the sense of boundary markers, indicating ”the limits of the Inner Sea that, for the Greeks, was the navigable world.”[p156]