Due to its remote, mountainous character, Arcadia has always been a classical refuge. So during the Dorian invasion, when Mycenaean Greek was replaced with Doric Greek along the coast of the Peloponnes, it survived in Arcadia, developing into the Arcadocypriot dialect of Classical Antiquity. Arcadocypriot never became a literary dialect, but it is known from inscriptions. One of the birthplaces reported for Zeus is Mount Lycaeum in Arcadia. Lycaon, a cannibalistic Pelasgian king, was transformed into a werewolf by Zeus. Lycaon's daughter was Callisto. It was also said to have been the birthplace of Zeus' son, Hermes, as well as Apollo and Diana.
Arcadia remained a rustic, secluded area, and its inhabitants became proverbial as primitive herdsmen leading simple pastoral unsophisticated yet happy lives, to the point that Arcadia may refer to some imaginary idyllic paradise, immortalized by Virgil's Eclogues, and later by Jacopo Sannazaro in his pastoral masterpiece, Arcadia (1504); see also Arcadia (utopia).
The Latin phrase “Et in Arcadia ego” – usually interpreted to mean "I am also in Arcadia" or "I am even in Arcadia" – is an example of “memento mori,” a cautionary reminder of the transitory nature of life and the inevitability of death. The phrase is most often associated with a 1647 painting by Nicolas Poussin, also known as "The Arcadian Shepherds" (Les Bergers d”Arcadie). In the painting below, the phrase appears as an inscription on a tomb discovered by youthful figures in classical garb. It has been suggested that the phrase is an anagram for the Latin phrase "I! Tego arcana Dei", which translates to "Begone! I keep God's secrets."
Nicolas Poussin (1593/94-1665)

Les Bergers d’Arcadie by Nicolas Poussin (circa 1650)
Nicolas Poussin was a French artist who moved to Rome and spent his career there. To literate people in the 17th century the name Arcadia readily evoked the pastoral tradition, that easy going genre of poetry that had developed in parallel with epic writing since the time of the classical Greeks. The tradition stems from the supposedly carefree, open-air life enjoyed by shepherds and shepherdesses who spent all summer guarding their flocks, thus giving them plenty of time in which to play their flutes and compose poetry.
The literary sources are numerous - from the Eclogues or Bucolics of Virgil to the Arcadia of Jacopo Sannazaro (1502) - all invoking an imaginary place, a "kingdom of Utopia". However the phrase ET IN ARCADIA EGO can not be traced to any known classical source. The Latin words means "Even in Arcadia I exist", where "I" is considered to refer to death.
The visual source for the painting is certainly found in its celebrated precursor by the Bolognese artist Guercino (1591-1666), painted around 1618-1620 and now in the Galleria Corsini, Rome. This was in all likelihood commissioned by the Florentine Barberini family, amongst the most important patrons of the arts in Rome, and notably cardinal Francesco Barberini who had commissioned "The Death of Germanicus". Was it this man who informed Poussin of the work by Guercino? Poussin painted several works based on Arcadia and Greek mythology, including “The Eleventh Task of Hercules” (below).

Le onzième Travaux d´Hercule by Nicolas Poussin
Claude Lorrain (1600-1682)
Another
French artist who spent his career in Rome was Claude Lorrain. He was born
Claude Gellee, near Nancy in Lorraine, in France. Originally trained as a pastry
chef, by age 13 he was in Italy working as a general studio assistant for
painters. He settled in Rome around 1617 and within ten years he had a secure
reputation as a landscape painter. He virtually reinvented landscape painting,
giving it a formula, varied with growing subtlety and imagination, which was to
become the principal pictorial approach to painting landscape for the next two
centuries. Claude's career spans almost the entire century - his earliest
datable works are from the end of the 1620s - and he witnessed almost all the
main changes of artistic style during his long stay in Rome.
Landscape with Aeneas at Delos (1672) by Claude Lorrain
The painting (above) is one of six paintings showing stories of Aeneas, the founder of Rome. Aeneas, in red; his father, Anchises, in blue; and the younger son, Ascanius, have arrived at Delos, the city of Apollo, having fled Troy, taking with them the sacred images of the gods. They are received by the priest/king Anius, in white, who showed them the city, the new shrines, and the sacred trees under which Apollo and Diana had been born.
Claude's earliest surviving pictures have usually been dated to around 1630, although he did not begin to keep accurate records until the mid-1630s. Then he decided to keep a record of every picture he painted, in the form of the Liber veritatis (British Museum, London), in which, after he had completed a painting, he made a careful drawing of the composition and noted the buyer on the back. He thus documented some two hundred pictures over almost fifty years.
Claude's achievement as a pioneer in landscape painting has earned him a place in the pantheon of art history. He was widely imitated for almost two centuries, and therefore often produces in the popular imagination a feeling of déjà-vu, especially in his best-known compositions. Claude's powers of innovation were in fact limited - he concentrated on a very narrow range of tones in a very narrow landscape type. Once he had perfected his technique, he did not develop much further deliberately; his work was too eagerly sought after by powerful patrons for him to need to do so.

Apollo and the Muses on Mount Helicon (1680) by Claude Lorrain
Both Poussin and Lorrain had a huge impact on landscape design. As a reaction against the strict geometry of the Renaissance and Baroque, every estate owner in England wished to recreate the dream of Arcadia on his own property. This was the beginning of the English Landscape Revolution. In 1720, Henry Hoare copied the design for his temple of Apollo at Stourhead Estate in England from the pastoral landscapes of Claude Lorrain.