The Ruins of St. Paul's refer to the façade of what was originally the Church of Mater Dei built in 1602-1640 and the ruins of St. Paul's College, which stood adjacent to the Church, both destroyed by fire in 1835. As a whole, the old Church of Mater Dei, St. Paul's College and Mount Fortress were all Jesuit constructions and formed what can be perceived as the Macao's 「acropolis」.

The façade of the Ruins of St. Paul's measures 23 metres across and 25.5 metres high and is divided into five levels. Following the classical concept of divine ascension, the orders on the façade on each horizontal level evolve from Ionic, Corinthian and Composite, from the base upward. The upper levels gradually narrow into a triangular pediment at the top, which symbolizes the ultimate state of divine ascension - the Holy Spirit. The façade is mannerist in style carrying some distinctively oriental decorative motifs. The sculptured motifs of the façade include biblical images, mythological representations, Chinese characters, Japanese chrysanthemums, a Portuguese ship, several nautical motifs, Chinese lions, bronze statues with images of the founding Jesuit saints of the Company of Jesus and other elements that integrate influences from Europe, China and other parts of Asia, in an overall composition that reflects a fusion of world, regional and local influences. Nowadays, the façade of the Ruins of St. Paul's functions symbolically as an altar to the city. The baroque/mannerist design of this granite façade is unique in China (as noted in UNESCO's Atlas mundial de la arquitectura barroca). The Ruins of St. Paul's are one of the finest examples of Macao's outstanding universal value.

Close by, the archaeological remains of the old College of St. Paul stand witness to what was the first western-style university in the Far East, with an elaborate academic programme that included Theology, Mathematics, Geography, Chinese, Portuguese, Latin, Astronomy and various other disciplines, preparing a significant number of missionaries to pursue Roman Catholic work in China, Japan and throughout the region. The missionary route followed by the Jesuits from Macao all over the region was crucial in facilitating the dissemination of Catholicism in China, Japan and other countries, also enabling a broader interchange in other scientific, artistic and cultural fields.

大三巴牌坊是天主之母教堂（即聖保祿教堂）正面前壁的遺址。

聖保祿教堂附屬於聖保祿學院。該學院於1594年成立，1762年結束，是遠東地區第一所西式大學，設文法學部、人文學部、倫理神學部等。由其培養的傳教士，除到日本、中國外，還到越南、泰國、柬埔寨等地傳教。

聖保祿教堂於1602年開始修建，現在牌坊左側還存有當時的奠基石。整個建築工程於1637至1640年間才完全竣工；目前所見的教堂前壁就是最後落成的部分。1835年，一場大火燒燬了聖保祿學院及其附屬的教堂，僅剩下教堂的正面前壁、大部分地基以及教堂前的石階。自此之後，這裡便成為世界聞名的聖保祿教堂遺址。本地人因教堂前壁形似中國傳統牌坊，將之稱為大三巴牌坊。

教堂後部遺址於1837至1854年被用作埋葬教士的墓地。

1990 至1996 年間，澳門政府對聖保祿教堂遺址進行考古、修復及再利用工程，由葡國建築師負責策劃和設計，多位考古學家、歷史學家和博物館學家參加工作，經過五年考古、勘察及建造，建成一間博物館，於1996年10 月落成。

建築描述：

大三巴牌坊的建築由花崗石建成，寬23米，高25.5米，上下可分為五層，自第三層起往上逐步收分至頂部則是一底邊寬為8.5米之三角形山花，整個牆壁是巴洛克式，但一些設計或雕刻，卻具有明顯的東方色彩，如中文字或象徵日本傳統的菊花圖案，這座中西合璧的石壁在全世界的天主教教堂中是獨一無二的。

牌坊第一層，即入口層，共有三個入口並有十枝愛奧尼柱式支撐及裝飾牆面，大門兩側各三枝，側門一邊各兩枝，小門門楣上有耶穌會會徽 IHS 的浮雕圖案，正門上則寫有「MATER DEI」，說明此教堂是供奉聖母；第二層相應是第一層之延續，牆壁由十枝科林新柱式及三個窗口組成，窗楣上均有七朵玫瑰花浮雕裝飾，中間窗口側兩柱間以棕欖樹裝飾，側窗洞兩邊柱間對稱設有壁龕，分別置有四位天主教聖人的銅像；第三層是裝飾最豐富的一層，並開始收分，牆中央設有一深凹之拱形壁龕，供奉聖母，兩側各有三個天使浮雕，此一層中央共有六枝混合式壁柱，兩側以方尖柱代替壁柱，是下面兩層柱體的延續，各柱間均以淺浮雕裝飾，左邊是智慧之樹和一隻七頭怪獸，其上有一聖母浮雕，側有中文「聖母踏龍頭」字樣，而右邊對稱位置上則是精神之泉及一隻西式帆船，上有海星聖母浮雕。在柱組外邊是一渦卷，右邊是一骷髏及中文字「念死者無為罪」；左邊則是一魔鬼浮雕，中文則是「鬼是誘人為惡」，此層最外側兩塊牆身是由兩條帶有圓頂之方尖柱，而牆側則設有中國舞獅造型的獅子，作滴水之用；在第四層是一耶穌聖龕，兩側有耶穌受難之刑具浮雕，往外由四枝混合式壁柱組成，柱間以天使淺浮雕點綴，柱兩邊有弧形山牆。第五層是一三角形山花，中間有一銅鴿，頂部設有十字架。