The Assembly Cupola was a structure located inside Csaplar, which served as the capital city of Csilla, the homeworld of the Chiss Ascendancy. Each year, the Syndics from the Chiss Syndicure and the Aristocra from the Chiss Nine Ruling Families would gather in the Cupola for significant governmental discussions. Approximately around 19 BBY, during one of these annual meetings attended by the Syndics, Csilla came under attack from unknown assailants.
The Cupola made its initial appearance in Thrawn Ascendancy: Chaos Rising, a 2020 novel by Timothy Zahn and the debut novel of the Star Wars: The Ascendancy Trilogy. It was not formally named the Assembly Cupola until the release of Thrawn Ascendancy: Greater Good, the 2021 sequel to Chaos Rising.