The Cathedral of San Carlos Borromeo, also known as the Royal Presidio Chapel, is a Roman Catholic cathedral located in Monterey, California, United States. The cathedral is the oldest continuously operating parish and the oldest stone building in California. It was built in 1794 making it the oldest (and smallest) serving cathedral along with St. Louis Cathedral in New Orleans, Louisiana. It is the only existing presidio chapel in California and the only existing building in the original Monterey Presidio.
The church was founded by the Franciscan Father Junípero Serra as the chapel of Mission San Carlos Borromeo de Carmelo on June 3, 1770. Father Serra first established the original mission in Monterey at this location on June 3, 1770, near the native village of Tamo. However, Father Serra became engaged in a heated power struggle with Military Governor Pedro Fages, who was headquartered at the Presidio of Monterey and served as governor of Alta California between 1770 and 1774. Serra decided to move the mission away from the Presidio, and in May, 1771, the viceroy approved Serra's petition to relocate the mission to its current location near the mouth of the Carmel River and the present-Day town of Carmel-by-the-Sea. The new mission was named Mission San Carlos Borromeo de Carmelo.
In 1849, the chapel was selected to be the Pro-Cathedral of the Diocese of Monterey by Bishop Joseph Alemany. After Alemany became Archbishop of San Francisco, his successor Thaddeus Amat y Brusi moved the cathedral to Mission Santa Barbara, to be closer to the population in Los Angeles.