The land that is today home to the Vatican City was formerly a marshy area that was drained in Roman times to prepare the land for the city, the gardens of Agrippina (mother of the Emperor) and numerous necropolises; one of the most famous is the resting place of the Apostle Saint Peter. After the passing of the Edict of Milan, the construction of the Basilica di San Pietro was officially initiated around 324 a.d; the foundations of which were developed around the tomb of the Saint. Naturally the original structure had no bearings on today’s building. Its construction took various centuries and saw the rule of numerous Popes and the participation of various architects who modified and added different elements and features. The Basilica represents the fulcrum of Christianity, as one of the most important destinations for pilgrims and it has very much determined the subsequent urban development of the area. It was Pope Leone IV who began to erect the city walls that established the basis for a separate state that was officially approved in 1929 with the Lateran treaty between the Kingdom of Italy and the Holy See. The centre of the Vatican City is currently Saint Peter’s Square, a colossal construction that every Sunday gathers hundreds of religious and inquisitive visitors from all over the world. The Square is bordered by rows of four columns; however from a certain part of the square the columns appear as one straight line instead of four. Inside the Basilica there are a number of famous works of art from all over the world including the famous "Pietá" and the Sistine Chapel that are both the work of Michelangelo. There are also numerous places of interest to visit inside the walls of the Vatican including a number of churches as well as palaces and archeological sites such as the Vatican necropolis. The most popular area is the Gardens and Vatican Museums. Two thirds of the Vatican City are made up by these gardens that were the creation of different artists such as Bernini and Tempesta who filled the area with fountains, statues and temples. The Vatican Museums host numerous works and objects with incredible historical and cultural value that the Church has accumulated over the centuries.