Volcanic activity first took place at Etna about half a million years ago, with eruptions occurring beneath the sea off the ancient coastline of Sicily. About 300,000 years ago, volcanism began occurring to the southwest of the summit (centre top of volcano) then, before activity moved towards the present centre 170,000 years ago. Eruptions at this time built up the first major volcanic edifice, forming a stratovolcano in alternating explosive and effusive eruptions. The growth of the mountain was occasionally interrupted by major eruptions, leading to the collapse of the summit to form calderas.
From about 35,000 to 15,000 years ago, Etna experienced some highly explosive eruptions, generating large pyroclastic flows, which left extensive ignimbrite deposits. Ash from these eruptions has been found as far away as Rome, 800 km (497 mi) to the north.
Thousands of years ago, the eastern flank of the mountain experienced a catastrophic collapse, generating an enormous landslide in an event similar to that seen in the 1980 eruption of Mount St. Helens. The landslide left a large depression in the side of the volcano, known as 'Valle del Bove' (Valley of the Ox). Research published in 2006 suggested this occurred around 8000 years ago, and caused a huge tsunami, which left its mark in several places in the eastern Mediterranean. It may have been the reason the settlement of Atlit Yam (Israel), now below sea level, was suddenly abandoned around that time.
The steep walls of the valley have suffered subsequent collapses on numerous occasions. The strata exposed in the valley walls provide an important and easily accessible record of Etna's eruptive history.
The most recent collapse event at the summit of Etna is thought to have occurred about 2,000 years ago, forming what is known as the Piano Caldera. This caldera has been almost entirely filled by subsequent lava eruptions, but is still visible as a distinct break in the slope of the mountain near the base of the present-day summit cone.
Mount Etna is one of the 16 Decade Volcanoes.
 Historical eruptions
Eruptions of Etna follow a variety of patterns. Most occur at the summit, where there are currently (as of 2008) six distinct craters—the Northeast Crater, the Voragine, the Bocca Nuova, and the Southeast Crater. Other eruptions occur on the flanks, which have more than 300 vents ranging in size from small holes in the ground to large craters hundreds of metres across. Summit eruptions can be highly explosive and spectacular, but rarely threaten the inhabited areas around the volcano. In contrast, flank eruptions can occur down to a few hundred metres altitude, close to or even well within the populated areas. Numerous villages and small towns lie around or on cones of past flank eruptions. Since the year AD 1600, at least 60 flank eruptions and countless summit eruptions have occurred; nearly half of these have happened since the start of the 20th century, and since 2000, Etna has had four flank eruptions—in 2001, 2002–2003, 2004–2005, and 2008-2009. Summit eruptions occurred in 2006, 2007–2008, January–April 2012, and again in July–October 2012
The first known record of eruption at Etna is that of Diodorus Siculus.
The Roman poet Virgil gave what was probably a first-hand description of an eruption in the Aeneid:
A spreading bay is there, impregnable To all invading storms; and Aetna's throat With roar of frightful ruin thunders nigh. Now to the realm of light it lifts a cloud Of pitch-black, whirling smoke, and fiery dust, Shooting out globes of flame, with monster tongues That lick the stars; now huge crags of itself, Out of the bowels of the mountain torn, Its maw disgorges, while the molten rock Rolls screaming skyward; from the nether deep The fathomless abyss makes ebb and flow.
— Virgil, Aeneid, edition of Theodore C. Williams, ca. 1908 [lines 569–579]
Portus ab accessu ventorum immotus et ingens ipse; sed horrificis iuxta tonat Aetna ruinis; interdumque atram prorumpit ad aethera nubem, turbine fumantem piceo et candente favilla, attollitque globos flammarum et sidera lambit; interdum scopulos avolsaque viscera montis erigit eructans, liquefactaque saxa sub auras cum gemitu glomerat, fundoque exaestuat imo.
— The same, in Virgil's Latin/
In 396 BC, an eruption of Etna reportedly thwarted the Carthaginians in their attempt to advance on Syracuse during the Second Sicilian War.
A particularly violent explosive (Plinian) summit eruption occurred in 122 BC, and caused heavy tephra falls to the southeast, including the town of Catania, where many roofs collapsed. To help with reconstruction after the devastating effects of the eruption, the Roman government exempted the population of Catania from paying taxes for ten years.
During the first 1500 years AD, many eruptions have gone unreported (or records have been lost); among the more significant are: (1) an eruption in about 1030 AD near Monte Ilice on the lower southeast flank, which produced a lava flow that travelled about 10 km, reaching the sea north of Acireale; the villages of Santa Tecla and Stazzo are built on the broad delta built by this lava flow into the sea; (2) an eruption in about 1160 (or 1224), from a fissure at only 350–450 m (1,148–1,476 ft) elevation on the south-southeast flank near the village of Mascalucia, whose lava flow reached the sea just to the north of Catania, in the area now occupied by the portion of the city named Ognina.
Etna's most destructive eruption since 122 BC started on 11 March 1669 and produced lava flows that destroyed at least 10 villages on its southern flank before reaching the city walls of the town of Catania five weeks later, on 15 April. The lava was largely diverted by these walls into the sea to the south of the city, filling the harbour of Catania. A small portion of lava eventually broke through a fragile section of the city walls on the western side of Catania and destroyed a few buildings before stopping in the rear of the Benedictine monastery, without reaching the centre of the town. Contrary to widespread reports of up to 15,000 (or even 20,000) human fatalities caused by the lava, contemporaneous accounts written both in Italian and English mention no deaths related to the 1669 eruption (but give very precise figures of the number of buildings destroyed, the area of cultivated land lost, and the economic damage), so it can be safely assumed that the enormous number of fatalities often picked up also by the news media must be a confusion with the earthquake that devastated southeast Sicily (including Catania) 24 years later, in 1693. A study on the damage and fatalities caused by eruptions of Etna in historical times reveals that only 77 human deaths are attributable with certainty to eruptions of Etna, most recently in 1987 when two tourists were killed by a sudden explosion near the summit.
[link to en.wikipedia.org