The subject of this article is a type of capital initial letter represented as if it were a three-dimensional object carved in metal. Its central ridge forms the spine of the letter which then seems to be hollowed on either side. It appears in manuscripts illuminated in Padua or Venice in the late 1450's. Outstanding examples are found in the well-known copy of Strabo's Geography in the Latin translation of Guarino, which was sent as a present by the Venetian condottiere Jacopo Marcello to Rene of Anjou in 1459. Millard Meiss once ascribed its invention to the Paduan painter Andrea Mantegna and named it "Littera Mantiniana" (Mantegna's letter) because he believed that the illuminator of Strabo's work was certainly Mantegna, while other scholars nowadays insist that it was invented by Veronese copyist Felice Feliciano. In this article, I observe its first examples in Geography of Strabo in the terms of the characteristic of its three-dimentionality, and analyze again the possibility of Mantegna or Feliciano as its inventor.