“Virtue is what makes man good, that is conforming to proper reason; this happens in three ways:
I. reason is corrected, and this a duty of intellectual virtues;
II. Corrected reason is applied to human things and this a duty of justice;
III. Impediments to the correct use of reason are removed whether they come from  attractions, and this is duty of temperance, or from difficulties, which is the task of strength: so even strength is therefore a virtue” (Thomas Aquinas, Summa Teologica, q. 123, 1).
Angelico specified that “Fortitude is applied when fear withdraws us from difficulties or when audacity would bring us to excesses: fortitude therefore represses fear and moderates  audacity” (II-II, q. 123, a.12).
Fortitude in Greco-Roman classical culture occupies an important position. Plato placed it amongst the fundamental virtues of the polis and of the person: in the polis it is the virtue of the warrior class, in the person it is the virtue of the irascible soul: “Strong….we call everyone when their irascible part through pain and pleasure preserves what has been defined as dangerous or not reasonable” (Republic, 442B). Aristotle identifies fortitude with courage and defines it “the correct means between impetuosity and cowardliness” (Ethical Nicomachea, 1115a, 6).
We can presume that there are not substantial differences in the concepts so far expressed about Fortitude by ancient people and Christian theologians. But unlike Greek thought, for which Fortitude represents a cosmic principle of blind nature, Jewish religiousness sets Fortitude and every energetic principle in a personal God, Lord of nature and history. From this vision doxologies begin that exalt, together with mercy and generosity, the uncontrollable strength of God’s arm: “Jahvé your God is the God of the gods, the God of lords, the great, strong, terrible God” (Deuteronomy, 10, 17). The “strong God” the “Strong of Israel” are names suitable to him. In the New Testament besides a quality of God, Fortitude also becomes a dowry of Christ, God's Child who has become flesh. Isaiah had denominated the future Emmanuel “strong God”, upon whom “the spirit of fortitude” would descend (Isaiah, 9, 5;11, 2).
The Fortitude of Christ reverberates on all Christians who are called in the First John Letter “ischyroi” (strong), because they are able to hold out against the temptations of Evil and sin thanks to the word of God that lives in them.
Saint Augustine adds that Fortitude consists of the “steadiness of mind” (firmitas animi), that is the ability to tolerate evil and the adversities of life in the sight of the enjoyment of the supreme good” (De Civitate Dei, XIX, c. 4).
The virtue of the warrior class, as described by Plato, is  referred to in the card of Strength in the Visconti Sforza Tarots deck that shows Hercules in what was considered his first labour, the struggle against the Nemean lion (figure 1). His twelve labours became the paradigm of the victorious hero against the violent strengths of nature and the brutality of man himself, as confirmed by a not well identified Albricus in the Vatican Mytograph III (Mai,1831, p.161) who considers them as actions of virtue “…id est virtus”, a quality attributed to the hero by different humanists, for which Hercules becomes symbol of humanity in its highest degree.
A second version of this triumph can be found in the Yale Visconti Sforza Tarots deck (figure 2) showing a young girl who opens the jaws of a lion with her hands, according to an iconographical root verifiable in the biblical narration of Samson and the lion of Tamna (Judges, 14, 5). (figure 3 - Virgil Solis, woodcutting, XVI century)  
Ripa writes about his version of Fortitude “A woman who with a club similar to that of Hercules suffocates a big lion, & at her feet there is a quiver with arrows, & arc; this figure I drew from a beautiful medal, see Peter in the book I” (Iconology, 1669, page 226).
The representation of Fortitude with the young girl who opens the lion’s jaws with her hands without the aid of a cudgel and in which physical strength and moral fortitude come to assume equal characteristics, was widely diffused in the Middle Ages: we should remember for instance the image of Fortitude represented in the Allegory of Virtues, of Vices and of Liberal Arts (figure 4) in the code ms. B42 N. f Novella super quinque libros decretalium by Niccolò da Bologna of the XIV century in the Ambrosian Library in Milan.  
A further iconographic version of “Strength / Fortitude” shows a young girl near to a column which is broken or still intact. The broken column comes once again from the story of Samson, destroyer of the temple of the God Dagon (Judges, 16,29) and it is represented in the Tarots of the Charles VI deck (figure 5).
According to Ripa the meaning of the entire column, which we find for instance in the Rosenwald Tarot deck (figure 6) and in the Tarocchino Bolognese deck (figure 7), can be sought in its specific function of supporting strength: “An armed woman, & dressed in the colour of a lion, a colour that means fortitude, since it is like that of the lion, this woman leans on a column, because this is the strongest among all of the parts of the building, since it sustains the others, at the feet of this figure, lies a lion an animal the Egyptians used, as can be read in many writings” (Iconology,1669, page 226).
Such interpretation brings us partly back to the Forteza of the Mantegna Tarots deck (figure 8). Although this column is broken, there are nonetheless various analogies with the description given by Ripa, among which the “armed woman”, “her dress the colour of a lion” (verifiable in the bodice with a lion’s face which the woman wore) and finally the presence of the beast that lies at her feet.
Another different representation characterises the card of Strength in the Rosenthal Tarots deck (an evidently nineteenth-century creation) where a mighty castle represents the impenetrable “fortitude”, favouring a linguistic simile typical of the late medieval tradition.