Today, a monumental ancient bronze pigna, or pinecone, rests on a marble capital in the Cortile della Pigna of the Vatican Museum in Rome. Modern viewers appreciate the pigna largely as a curiosity, but what is often overlooked by the casual visitor and the art historian alike is the sculpture's rich history and the meanings it amassed over the two thousand years it spent in the vicinity of the Ager Vaticanus. The exact origins of the pigna are a mystery, but early renovations to the church of Old St. Peter's in Rome suggest that the sculpture once served as the essential and unifying water feature of a fountain located in the center of the atrium of the church no later than c. 752-57. In this thesis, I focus on the pigna's eighth-century incorporation into the atrium of Old St. Peter's and examine the fountain's symbolic value within the architectural ensemble of which it once formed an essential part. This study explores the pigna's soteriological meaning, and suggests that the addition of the pigna sculpture transformed the pre-existing atrium into the embodiment of an earthly and celestial Paradise. To demonstrate this, I show how the addition of the pigna led to the creation of a new architectural term--the paradiso--that designated the physical and spiritual significance of the space. I focus on issues of medieval reception, suggesting that the pigna sculpture inspired, shaped, and completed the paradiso in the minds of eighth-century viewers through its form, function, and basic botanic identity. This study contributes a greater understanding of the pigna's Christian significance, and suggests that the pigna sculpture's addition to the atrium in the eighth century reflected the church's emergent status as a center for pilgrimage and papal influence.