In 1290, Denis began to pursue the systematic centralisation of royal power by imposing judicial reforms, instituting the Portuguese language as the official language of the court, creating the first university in Portugal, and ridding the military orders in the country of foreign influences. His policies encouraged economic development with the creation of numerous towns and trade fairs. He advanced the interests of the Portuguese merchants, and set up by mutual agreement a fund called the Bolsa de Comércio, the first documented form of marine insurance in Europe, approved on 10 May 1293. Always concerned with development of the country's infrastructure, he encouraged the discovery and exploitation of sulphur, silver, tin and iron mines and organised the export of excess production of agricultural crops, salt, and salted fish to England, Flanders, and France.
Denis signed the first Portuguese commercial agreement with England in 1308, and secured a contract in 1317 for the services of the Genoese merchant sailor Manuel Pessanha (Portuguese form of the Italian "Pezagno") as hereditary admiral of his fleet, with the understanding that Pessanha and his successors should provide twenty Genoese captains to command the king's galleys, thus effectively founding the Portuguese navy.
In 1289 Denis had signed an agreement with Pope Nicholas IV, swearing to protect the Church's interests in Portugal. When Pope Clement V allowed the annihilation of the Knights Templar throughout most of Europe on charges of heresy, Denis created in 1319 a Portuguese military order, the Order of Christ, for those knights who survived the purge. The new order was designed to be a continuation of the Order of the Temple. Denis negotiated with Clement's successor, John XXII, for recognition of the new order and its right to inherit the Templar assets and property.