construction was carried on during different periods and often far apart, the walls were not built according to any uniform plan. Improvements continued during the terms of the succeeding Governor-Generals. Governor-General Juan de Silva executed certain work on the fortifications in 1609 which was improved by Juan Niño de Tabora in 1626, and by Diego Fajardo Chacón in 1644. The erection of the Baluarte de San Diego was also completed that year. This bastion, shaped like an "ace of spades" is the southernmost point of the wall and the first of the large bastions added to the encircling walls, then of no great height nor of finished construction. It was the former site of Nuestra Señora de Guia, the very first stone fort of Manila. Ravelins and reductos were added to strengthen weak areas and serve as outer defenses. A moat was built around the city with the Pasig River serving as a natural barrier on one side. By the 18th century, the city was totally enclosed. The last construction works were completed by the start of the 19th century. Inside colonial Intramuros The main square of the city of Manila was Plaza Mayor (later known as Plaza McKinley then Plaza de Roma) in front of the Manila Cathedral. East of the plaza was the Ayuntamiento (City Hall) and facing it was the Palacio del Gobernador, the official residence of the Spanish viceroyalties to the Philippines. An earthquake on June 3, 1863, destroyed the three buildings and much of the city. The residence of the Governor-General was moved to Malacañang Palace located about up on the Pasig River. The two previous buildings were later rebuilt but not the Governor's Palace. Inside the walls were other Roman Catholic churches, the oldest being San Agustin Church (Augustinians) built in 1607. The other churches built by the different religious orders – San Nicolas de Tolentino Church (Recollects), San Francisco Church (Franciscans), Third Venerable Order Church (Third Order of St. Francis), Santo Domingo Church (Dominican), Lourdes Church (Capuchins), and the San Ignacio Church (Jesuits) – has made the small walled city the City of Churches. Intramuros was the center of large educational institutions in the country. Convents and church-run schools were established by the different religious orders. The Dominicans established the Universidad de Santo Tomás in 1611 and the Colegio de San Juan de Letrán in 1620. The Jesuits established the Universidad de San