羅馬帝國時期複製希臘化時期的畫作中出現了整片藍綠色的天空，然進入基督教信仰的中世紀時期，此整片藍天的風格並未見普及或進一步往寫實方向發展，反而是朝向描繪具象徵性的天國。聖經描述耶和華不僅是出現於天上的雲端，亦坐在穹蒼上繞著虹的天國寶座，全身有如火，周圍有光輝，如雲中虹的形狀。在漫長的中世紀時期，教堂或墓室的嵌畫設計者，對此既是天空又是具象徵性天國的描繪各有不同。其中以三一三年基督教成為合法宗教以來，至七三○年發起偶像破壞運動，這期間的天空或天國描繪最傑出且具變化，偶像破壞運動廢止後至中世紀末期的天空或天國風格皆受此時期影響而極少更改，並且較多直接以金色背景象徵天國。本文重點在於探討三一三年至七三○年間基督教嵌畫上如何呈現天空或天國景象，經分析探得以藍色或金色為背景加長條狀多色雲彩是此時期嵌畫中用來象徵天空或天國的最大特徵，然其間風格亦有些差異。四世紀出現在白色背景上加簡單的長條狀多色雲彩象徵天國，五世紀則主要以藍色背景加長條狀多色雲彩。五世紀中期出現全然以金色為背景象徵光輝的天國，六世紀則有漸多以金色為背景加上長條狀多色雲彩代表光輝多彩的天國。七世紀或八世紀初則分別在藍色和金色背景上，出現了帶花邊的長條形和三角形多色雲彩。長條狀多色雲彩為何盛行於四至七世紀，又明亮的金色背景為何出現於五世紀，且六世紀以來漸普及，其主要原因應是此時期的信徒們相信聖經中的記載－虹圍著寶座，周圍有光輝，如雲中虹。

　　　　　This study tries to explore how the designers of mosaic during A.D. 313 to 730 depicted skies, while Christianity almost dominated the whole western civilization. According to the Bible, the Lord came down in the cloud, was sitting on a throne in heaven, looked like fire, and brilliant light surrounded him; also a rainbow encircled the throne and the appearance of a rainbow in the clouds represented the Lord. By comparing the depictions of heaven in the Bible with those in the mosaics during 313-730, we realize that those in the mosaics roughly formed a certain function, meaning and style which were mainly inspired by the Bible. The simple and colorful belt-shaped clouds to represent heaven emerged in the fourth century, and at that time they were added to the white background, but during the fifth century they were mainly added to the blue background. Also the bright golden background as the symbol of the brilliant heaven appeared around the middle of the fifth century, and since then the golden background was getting popular. Later, during the seventh or early eighth century, the triangle-shaped clouds also become known to represent heaven. The blue or golden background with the colorful belt-shaped clouds might be the major characteristic of the mosaics to symbolize the heaven during 313 to 730.