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While it is not possible to identify exact sources for the square tables that Johannes Trithemius and, after him, Blaise de Vigenère presented in their cryptographic publications, there is good evidence that Trithemius may have been influenced by a variety of materials: He knew the figural poetry of Rabanus Maurus (780-856) that frequently used squares with a grid of 36 letters; he was fully aware of the medieval ars combinatoria and the works of the Mallorcan philosopher and theologian Raymundus Lullus (1233-1316), where he would have also found combinatorial circular disks; and he may have discerned a pattern for his square table in the medieval Easter or Lenten tables used for the calculation of the forty days of Lent and the days of Easter over a period of years.