Isidore of Seville (Cartagena, ca. 560 – Seville, 4 April 636) was a theologian, writer and Roman archbishop, as well as one of the most important figures of medieval culture; a Doctor of the Church, he is venerated as a saint by the Catholic Church. Born into an ancient Roman family, he succeeded his brother Leander as Archbishop of Seville (600 A.D.), the most authoritative ecclesiastical figure in Spain at the time.
He played a fundamental role in the political and religious affairs of Visigothic Spain, contributing to the conversion of the Visigoths from Arianism to Christianity, and convened and presided over important councils, such as those of Seville (619 and 625) and above all the Fourth Council of Toledo (633), which unified the Spanish liturgy and defined important Trinitarian and Christological formulas against the Priscillianists.
On an academic level, he is considered one of the greatest exponents of medieval culture and played a crucial role in preserving the knowledge of antiquity from being lost, thanks to his extraordinary work as a compiler.
Drawing upon classical, late Roman and Christian authors and sources, he gathered and organized the knowledge of his age in his most famous work, the Etymologiae sive Origines, published in 639 in twenty books.
The work is a true encyclopedia of knowledge, in which different disciplines—from grammar to law, from medicine to history and theology—are explained beginning with the etymological origin of words, according to the idea that understanding words allows a deeper understanding of reality.
The Etymologiae, widely copied by scribes, were second only to the Bible in circulation throughout the Middle Ages.They constituted a fundamental educational tool, contributing decisively to the preservation and transmission of Roman culture and profoundly influencing European culture for more than a thousand years, eventually becoming a model for dictionaries and encyclopedias of the Early Middle Ages and the Renaissance. In Book XIII of the Etymologiae, entitled De mundo et partibus (On the World and Its Parts), Isidore presents a true manual of physical geography and cosmography, offering a synthesis of ancient knowledge about the world, the heavens, the lands and the seas. In particular, in the sections De aestu maris and De fretis (On Tides and Straits), dedicated to the periodic movement of waters and the configuration of the narrowest and most dangerous sea passages, the author elevates Scylla as the symbolic place of the dangers of straits, seas and the force of waters. Its recognizability allows Isidore to isolate a paradigmatic case, making the risks of maritime passages concrete and recognizable, while blending natural explanations and mythical tradition within the framework of world geography.

“Tides are proper to the Ocean; a strait, however, is situated between two seas. The term aestus, that is, tide, refers to the movement of the sea’s ebb and flow, that is, its instability, from which also comes the name aestuarium given to places where the sea alternately enters and withdraws. The fretum, that is, the strait, is so called because within it the sea always fervet, that is, rages as if boiling. A strait, indeed, is a narrow arm of the sea and, as it were, fervens, that is, boiling, its name deriving precisely from the turbulence of the waves: such is, for example, the Strait of Cádiz or that of Sicily. According to Varro, straits were called freta as though to say fervida, that is, fervent and endowed with movement characteristic of boiling.
The origin of the name Regio given to the Strait of Sicily, according to Sallust, is the following. In ancient times Sicily would have been joined to Italy, forming with it a single landmass. Its central part would have been covered by water because it was very low, or it would have broken apart because it was very narrow, whence the name Pryiov, which in Greek means violently separated, broken. It is, in fact, a very narrow stretch of sea, only three miles wide, separating Sicily from Italy, sadly famous for the fabulous monsters represented on either side by Scylla and Charybdis. The inhabitants of those places call Scylla a cliff overlooking the sea which, when seen from afar, resembles the famous creature. They imagined it as a monster with a human body surrounded by canine heads also because the waves, breaking against it, seem to emit barking sounds. Charybdis was so named because it swallows ships into invisible whirlpools: it is, indeed, a turbulent point of the sea from whose depths emerge the wreckage of shipwrecks. Three times a day it raises the waves and three times it swallows them; for it receives the waters only to release them violently, and releases them violently only to receive them again.”

In this passage, Isidore distinguishes between two marine phenomena: tides and straits.
The tide, or aestus, is described as the cyclical movement of the sea’s ebb and flow; the strait, or fretum, is instead characterized by a continuous and turbulent movement of the waters, which boil and surge, a definition etymologically connected to the term fervens.
Isidore cites Varro to support the idea that the name freta means “boiling places,” emphasizing the intrinsic movement of the waters.
Particular attention is devoted to the Strait of Sicily, for which Isidore also invokes Sallust: this strait is associated with the mythological figures of Scylla and Charybdis, which embody the dangers of navigation.
It is, however, Scylla that captures attention: recalling the image of a monster with a human body and canine heads, her rock, the waves surrounding it and the incessant noise of the waters combine to make her the heart of the strait, the emblem of the sea’s violence and the difficulty of navigation.
From an analytical point of view, the mention of Scylla serves several functions.
First, it constitutes a concrete example of the phenomenon of straits, summarizing the typical characteristics of such places: narrowness, violent currents and dangers to navigation. Secondly, Scylla is elevated as the emblematic place of all dangerous straits, allowing Isidore to generalize the phenomenon he observed in the Strait of Sicily to all analogous passages.
Finally, the reference to myth makes it possible to combine natural observation, classical tradition and linguistic explanation, demonstrating Isidore’s encyclopedic method, which integrates literary sources and concrete data.
In summary, the passage does not merely describe tides and straits, but uses Scylla as the focal point of the argument, serving both to illustrate physical phenomena and to provide a symbolic understanding of treacherous maritime places.
Scylla therefore represents, in an exemplary manner, the universal model of straits characterized by turbulence and danger.

Giuseppe Ribuffo