Final answer:
A flat or vaulted ceiling of decorative character is known as a dome, with early examples like the barrel and ribbed vaults seen in Romanesque and Gothic architecture respectively, often adorned with frescoes.
Step-by-step explanation:
A flat or vaulted ceiling of decorative character is referred to as a dome. Early construction methods like those seen in Romanesque architecture utilized wood for roofing because the technique to span structures with stone wasn't fully developed, leading to innovations such as the barrel vault and ribbed vaulting. These vaults eventually became highly ornamental, particularly in Gothic architecture, where the ribbed vaulting created a distinctive pointed arch. Domes and vaults also were elaborately decorated with frescoes, using religious imagery and narratives to educate an illiterate population, sometimes enhanced with gold to reflect candlelight and enhance the interior lighting of the space. The development of stone and brick vaults, like the ribbed groin vaults seen in Gothic architecture, signify a notable advancement, offering not just structural benefits but also a decorative feature to the buildings.