1. Portuguese Policy of Secrecy or Silence. This controversial historical thesis, formulated in the first quarter of the 20th century by various historians, primarily Portuguese, states that Portugal made many voyages and discoveries in the Atlantic Ocean, including the discovery of the Americas sometime before 1492, but chose to keep those discoveries secret.
Before the 19th century, the historical record contains many gaps and breaks. This condition certainly applies to the surviving records from the Great Age of Discovery. None of the original logs for Christopher Columbus's four voyages survived, although a partial transcript exists for the first voyage. John Cabot's voyages to North America in 1497 are practically without any contemporary documentation and the same situation applies to Bartolomeu Dias's discovery in 1487 of the Cape of Good Hope. Such losses of primary sources are tragic but all too common and they usually occur quite innocently as the result of accidents or neglect. Some historians, however, have questioned whether the gaps in the Portuguese records are all that random. They suggest that some design or policy may lie behind the disappearance of some documents.
The thesis of a deliberate and systematic Portuguese government policy of secrecy concerning overseas exploration is a product of 20th-century historians. Jaime Cortesao, a Portuguese historian, first formulated the thesis in 1924. He contended that the surviving Portuguese chronicles about overseas explorations show definite signs of truncation and censorship.
If one is inclined to believe Cortesao, quite a lot of information was suppressed, including a Portuguese discovery of America prior to 1448. Jaime Cortesao was not alone in his support for the existence of a policy of secrecy. In Portugal the thesis has become a historical orthodoxy and a pillar of national pride. School textbooks at all levels teach it as fact. Lisbon's city government has even decorated its Avenida de Liberdade with a mosaic inscription which reads "Descoberta da America 1472 Joao Vaz Corte - Real Descobridor da America."
Outside of Portugal, historians, including Samuel Eliot Morison, generally reject Cortesao's thesis of a policy of secrecy and its various claims of monumental but previously uncredited Portuguese achievements during the 15th century. Dissent exists even in the Portuguese historical community where the respected historian Duarte Liete attacked Cortesao's theory as early as 1936. But in spite of all the controversy, the thesis of a Portuguese policy of secrecy still possesses enthusiastic supporters, and so continues to attract equally determined opponents.
The basic complaint of skeptical historians concerning the policy of secrecy is the almost complete absence of solid evidence for its existence. Historians admit that monarchs and countries throughout history have attempted to protect their overseas commerce by maintaining secrecy about the how and the where of their sources. But ultimately these efforts have failed. Supporters of the policy of secrecy reply that the lack of evidence is in itself evidence of the existence of a policy of secrecy that was extremely effective. Of course, their opponents, particularly Samuel Eliot Morison, find such an argument both circular and ridiculous. Ultimately Morison feels that Cortesao's thesis requires the Portuguese to maintain their secrets apparently for the sake of secrecy alone and often against their own best interests. He rightly argues that the Portuguese government's pursuit of a policy of secrecy needs to make sense and be of benefit to the national interests. If Portugal already knew about the Americas before 1492, why did Joao II abdicate virtually all of that new land to Spain in the Treaty of Tordesillas?
Another argument repeatedly brought to bear against the existence of such a policy of secrecy is the well documented and sustained participation of a substantial number of foreigners in Portugal's overseas explorations. Martin Behaim of Germany and Christopher Columbus of Genoa are simply the best known of a host of foreigners who served in Portugal's overseas ventures. With so many foreigners involved in Portugal's overseas enterprises, it would have been impossible to keep important discoveries a secret. Details of Portugal's jealously guarded African trade leaked out with amazing rapidity. Furthermore, little attempt was made to keep secret Bartolomeu Dias's discovery of the Cape of Good Hope in 1487 or Vasco da Gama's voyage to India in 1497. Why did the Portuguese let these important discoveries become public knowledge if they had such an effective policy of secrecy? Not surprisingly, outside of Portugal, the thesis of the policy of secrecy and its accompanying suppression of information about various discoveries, most notably a pre-Columbian discovery of America, has found little support among historians.