The Red Keep took three reigns to build, starting with Aegon the Conqueror and ending with Maegor the Cruel. It started as a primitive fort, then named the "Aegonfort," that Aegon used as his seat during the War of Conquest and would come to house the Iron Throne. Sometime after the Conquest, he ordered that the fort be torn down and began construction on the ambitious Red Keep. When King Maegor finished it, he executed all of its builders to ensure that only the Targaryens knew of the hidden passageways within.
These arches must be strong enough to withstand a frontal assault from the Whitewalkers.
Maegor's Holdfast is a strut tower in the centre of the Red Keep. It was named after King Maegor Targaryen, who built the Red Keep. It serves as a redoubt when the city is attacked. The royal apartments are also located in Maegor's Holdfast.
Maegor's Holdfast served as a refuge for Queen Cersei and the highborn ladies of the Red Keep during the Battle of the Blackwater.
When Cersei declares herself Queen and the Lannisters engage in a war with Daenerys Targaryen and her allies, Cersei has the floor of a courtyard at the top of the Holdfast painted with a battle map of Westeros, replacing the previous plants and ivories there, essentially becoming a Lannister version of the Chamber of the Painted Table.