I stole this from http://thecastros.org/history/history.htm
“Origin of the Castro Surname
Castro is the name of one of the oldest and most distinguished families in Spain. The original bearer of the name Castro, which is a local surname, once lived, held land, or was born in one of the places named Castrothe, which is the name of many places in Spain. The place-name Castro is derived from the Latin word ‘castrum’, which means ‘fortress’. During the Reconquista, there were numerous fortresses in the Iberian Peninsula that were used as a refuge for the Christian troops who fought against the Muslim Moors. The fortresses also protected the civilian population and the new settlers in the area. From the diverse regions of Spain come distinguished family names which have carried the proud heritage of Hispanic culture worldwide. The name Castro was traced to its source in Castile, an important kingdom of medieval Spain.
Although in comparison with other European surnames most Spanish names have changed very little, the variations Castro, Castrillo, Castrel do share the same heritage.
Around 3000 B.C. Iberians migrating from north Africa settled in the peninsula that is now home to Spain and Portugal. The Celts came southwest from Europe in the 14th century B.C. and settled in the north and west, in what are now the lands of Galicia and Portugal. In the 12th to 7th centuries B.C., Phoenician and Greek traders visited the peninsula, followed later by the Carthaginians.
In the 6th and 5th centuries B.C. Carthaginian traders supplanted the Greeks and pushed the Iberians farther inland. The 2nd Punic War, which began in 219 B.C., destroyed Carthage and gave Rome control of the peninsula. By this time the Celtic and Iberian cultures had intermingled in the central tableland to form a Celtiberian people. The Celtic, Iberian and Celtiberian tribes whom the Romans encountered in the 3rd century B.C. were not homogeneous groups. The Lusitanians, Galicians, Asturians, Cantabrains, Basques, and the Pyrenean tribes had different languages and religions. It took the Romans over 200 years to pacify the all of the peninsula’s fiercely independent tribes.
Rome encouraged its conquered lands to adopt its language and customs, and many Roman colonists settled in the Iberian peninsula. Over time the peoples of Rome and Hispania merged to form a Hispano-Roman culture. A long and close association with Rome laid the foundations upon with peninsular civilization was developed.
Following the decline of the Roman Empire in the 5th century A.D., the Visigoths came to control the peninsula, followed by the Muslims in 711. Aside from a small area in the north, Muslim victory was complete by 718. Over the centuries, however, the Christian population expanded to the south. By the 13th century the Christians had re-conquered all but Granada, which was finally taken in 1492 by Ferdinand and Isabella.
The Castro family originated in Castile, where they are thought to be descended from the earliest kings. Some of the oldest records of the name date from the early thirteenth century: Alvaro de Castro (died 1239) was a soldier of the Reconquest who fought under King Ferdinand III. The name also appears in a Papal Bull dating from 1242: the family is listed third below that of the King, an indication of its prominence. From Castile the family branched to other regions of the Christian north, including Leon, Galicia and Aragon. As the Reconquest progressed southwards, so did the family, and the family members took part in the re-conquering of the most important city of Cordoba in 1236. The Repartimiento de Cordoba of the 1240’s allotted lands and titles to those who had fought for the crown, and thus the family became established there, as well as in other major centres of the southern peninsula. Prominent among members of the family were fourteenth century nobleman Fernando de Castro, brother-in-law of King Peter I; fifteenth century nobleman Fadrique Castro, Count of Trasamara; sixteenth century Spanish theologian Alfonso de Castro; Spanish Golden Age playwright Guillen de Castro; eighteenth century Mexican philosopher and mathematician Agustin Castro; eighteenth century Spanish sculptor Felipe de Castro; nineteenth century Peruvian patriot Jose Felix Castro, who fought with Boliva in the war of independence; nineteenth century Spanish politician and diplomat Alejandro de Castro; nineteenth century Spanish poet Rosalia de Castro.
The Surrender of Granada freed Ferdinand and Isabella to begin the work of expansion. 1492 is a milestone in world history, when Columbus voyaged to the west, beginning an era of exploration which brought Spain power and prestige. Columbus’ discover was closely followed by further exploration and by the conquest and colonization of new territories.
The captains of the conquest of New Spain, Cores, Pizarro, Valdivia, and Balbo, led the conquistadors to wealth and adventure. Some of the first settlers were members of the Castro family. Vaca de Castro, a judge, was sent from Spain to Peru in 1541 by Charles V to advise Pizarro concerning the government of his province. Among the many migrants to the New World bearing this surname were Juan Castro, who sailed to Guatemala in 1536; Martin de Castro to America in 1513; Melchor de Castro to Florida.Sebastiano de Castro to Peru in 1535; and Pero Castro to America in 1513. More recently Latin American families have migrated to the United States and Canada. These developments have been the result of political or economic instability in the countries from which they originated.
Some of the most prominent family members include Spanish linguist and historian Americo Castro; Argentinian historian Ramon de Castro Esteves; Mexican writer and diplomat Antonio Castro Leal; Venezuelan politician Cipriano Castro; Cuban head of stateFidel Castro; Chilean poet and novelist Oscar Castro; American athlete Margaret Castro Gomez, 1988 Olympic bronze medalist for judo; Amando Alejandro Castro, Pilippine economist; Raul Castro, American Lawyer, politician and diplomatist; Real Admiral Ramon Castro Jijon, Ecuadoran naval officer and politician; Bill Castro, American government official; George Castro, American scientist; Jaime Castro, American graphic designer and television specialist.”
A Familia Castro 