The gradual spread of the use of fire-arms in the fourteenth and fifteenth centuries made mediaeval fortifications less effective. The initial response to the emergence of heavy artillery was to make the walls thicker. Some very different examples can (or could) be found in Gipuzkoa of this sixteenth century transition from the mediaeval fortification to the modern one: Gazteluzar in Irun, St. Elizabeth's Castle and the Tower in Pasaia, Charles V's castle and St. Elmo's Castle in Hondarribia and Holy Cross Castle in San Sebastian.