The history of Toompea is closely linked to the history of rulers and power in Estonia. Today Toompea is the center of the Government of Estonia and the Riigikogu (parliament), both of which are often simply referred to as Toompea. The location of the Riigikogu is the Toompea Castle, situated in the southwestern corner of the hill and topped by the Tall Hermann tower. The flag on the top of the tower is one of the best-known symbols in Estonia of the government in force.
Toompea is part of the Tallinn Old Town UNESCO World Heritage Site.
Geologically Toompea is associated with the North Estonian Klint (itself a subsection of the Baltic Klint). A separate relic klint island, Toompea lies about 1.5 km northwest of the North Estonian Limestone Plateau. The plateau and Toompea are connected with a gently sloped sandstone ridge. From the east, north and west Toompea is bordered for 1.5 km by a cliff with a height of up to 25 m. The southern slope of the hill descends more gently. The upper layer of the hill consists of Ordovician limestone (thickness about 5 m), which is also the main rock exposed at the cliff. However, most of the cliff face has been hidden behind a protective wall and only a few outcrops are left.
Toompea first emerged as an island from the Baltic Ice Lake around 10,000 years ago. Due to steady post-glacial rebound it became connected with the mainland during the early Littorina Sea stage. At 5,000 BCE the sea still reached the foot of the cliffs of Toompea. The modern coastline is at a distance of more than 1 km from Toompea and the foot of the hill lies at 17–20 m above sea level. The hill reaches about 48 metres (157 ft) in elevation.
Linda mourned for Kalev for one month after another till three months had passed, and the fourth was far advanced. She heaped a cairn of stones over his tomb, which formed the hill on which the Cathedral of Revel now stands. English translation by W.F. Kirby, 1895 
The first stronghold is believed to have been built on the hill in either the 10th or 11th century by residents of the ancient Estonian county of Revala. The late Iron Age fortified settlement did not probably have permanent inhabitants, but was rather seasonally used for protecting the harbour and its adjacent marketplace. The exact location of the stronghold is not known, but it is presumed that it occupied only a small portion of Toompea, either its then-highest point a bit southeast of today's cathedral or the northern end of the hill. Early archaeological evidence from the hill dates mainly to the second half of the 12th century and first half of the 13th century. Smaller amounts of older finds support the view that the stronghold might have been established already during the Viking Age.