Peter Brown, in his definitive Augustine of Hippo: A Biography (Revised 2000) wrote of St. Augustine's home in Hippo and his fear of the sea at pages 184-185:
"To reach the part of the town where Augustine lived in his 'Christian quarter', consisting of his main church with adjacent baptistry, a chapel, the bishop's house, and perhaps a monastery in a building overlooking the bishop's garden, you would have had to leave the main hill, and would have walked a good half mile towards the harbour. . . .
Yet, like so many ancient men, Augustine feared the sea. He never dared to sail along the rocky coast to Carthage; he always regarded the seaborne merchant as a speculator, taking the most hair-raising risks."
In the Thirteenth Book of Confessions (here, Albert C. Outler, Ph.D., D.D.'s translation for Nelson's Royal Classics), St. Augustine's view of the sea reflects that sense of the sea's fearful danger, drawing from Psalm 124 and Gen. 1:2:
"How can I speak of the weight of concupiscence that drags us downward into the deep abyss, and of the love that lifts us up by Thy Spirit who moved over the waters? To whom shall I tell this? How shall I tell it? For concupiscence and love are not certain 'places' into which we are plunged and out of which we are lifted again. What could be more like, and yet what more unlike? They are both feelings; they are both loves. The uncleanness of our own spirit flows downward with the love of worldly with the love of worldly care; and the sanctity of Thy Spirit raises us upward by the love of release from anxiety -- that we may lift our hearts to Thee where Thy Spirit is 'moving over the waters.' Thus, we shall have come to that supreme rest where our souls shall have passed through the waters which give no standing ground." [footnotes omitted]
In his Commentary on the Psalms (Christian Classics Ethereal Library), St. Augustine said more about Psalm 124:
5. In the first place, what meaneth, “Perchance our soul hath passed over”? (ver. 5).
Understand however the meaning to be this: “Thinkest thou our soul hath
passed over?” and why do they say, “Thinkest thou”? Because the
greatness of the danger maketh it hardly credible that he hath escaped.
They have endured a great death: they have been in great dangers; they
have been so much oppressed, that they almost gave consent while alive,
and were all but swallowed up alive: now therefore that they have
escaped, now that they are secure, but still remember the danger, the
great danger, say, “Thinkest thou our soul hath passed over the water
without substance?”
6. What is the water without substance, save the
water of sins without substance? For sins have not substance: they have
destitution, not substance; they have want, not substance. In that
water without substance, the younger son lost the whole of his
substance…Dost thou wish to see how the water is without substance?
Take away with thee to the world below what thou hast acquired: what
wilt thou do? Thou hast acquired gold: thou hast lost thy faith: after
a few days thou leavest this life; thou canst not take away with thee
the gold thou hast acquired by the loss of thy good faith; thy heart,
destitute of faith, goeth forth into punishment—thy heart, which if
full of faith, would go forth unto a crown. Behold, what thou hast done
is nothing: and thou hast offended God for nothing.
7. Men hear that common proverb; and the proverbs of God slumber in them. What proverb? “Better in hand than in hope.”
Unhappy man, what hast thou in hand? Thou sayest, “Better in hand.”
Hold it so as not to lose it, and then say, “Better in hand.” But if
thou holdest it not, why dost thou not hold fast that which thou canst
not lose? What then hast thou in hand? Gold. Keep it in hand,
therefore: if thou hast it in hand, let it not be taken away without
thy consent. But if through gold also thou art carried where thou
wishest not, and if a more powerful robber seeketh thee, because he
findeth thee a less powerful robber; if a stronger eagle pursue thee,
because thou hast carried off a hare before him: the lesser was thy
prey, thou wilt be a prey unto the greater. Men see not these things in
human affairs: by so much avarice are they blinded…
8. Let them escape the water without substance,
and say, “Blessed be the Lord, who hath not given us over for a prey
unto their teeth” (ver. 6).
For the hunters were following, and had placed a bait in their trap.
What bait? The sweetness of this life, so that each man for the sake of
the sweetness of this life may thrust his head into iniquity, and be
caught in the trap. Not they, in whom the Lord was, they who say, “If
the Lord Himself had not been in us;” they have not been taken in the
trap. Let the Lord be in thee, and thou wilt not be taken in the trap."
In Book XX, Chapter 16 of The City of God, St. Augustine spoke of the "sea of glass" in Rev. 15:2, saying that the sea symbolized "the surgings and restlessness of human life." Here is the entire chapter:
"Having finished the prophecy of
judgment, so far as the wicked are concerned, it remains that he
speak also of the good. Having briefly explained the Lord’s
words, “These will go away into everlasting punishment,” it
remains that he explain the connected words, “but the righteous
into life eternal.” “And I saw,” he says, “a
new heaven and a new earth: for the first heaven and the first
earth have passed away; and there is no more sea.” This
will take place in the order which he has by anticipation declared
in the words, “I saw One sitting on the throne, from whose face
heaven and earth fled.” For as soon as those who are not
written in the book of life have been judged and cast into eternal
fire,—the nature of which fire, or its position in the world or
universe, I suppose is known to no man, unless perhaps the divine
Spirit reveal it to some one,—then shall the figure of this world
pass away in a conflagration of universal fire, as once before the
world was flooded with a deluge of universal water. And by this
universal conflagration the qualities of the corruptible elements
which suited our corruptible bodies shall utterly perish, and our
substance shall receive such qualities as shall, by a wonderful
transmutation, harmonize with our immortal bodies, so that, as the
world itself is renewed to some better thing, it is fitly
accommodated to men, themselves renewed in their flesh to some
better thing. As for the statement, “And there shall be no more
sea,” I would not lightly say whether it is dried up with that
excessive heat, or is itself also turned into some better
thing. For we read that there shall be a new heaven and a new
earth, but I do not remember to have anywhere read anything of a
new sea, unless what I find in this same book, “As it were a sea
of glass like crystal.” But he was not then speaking of
this end of the world, neither does he seem to speak of a literal
sea, but “as it were a sea.” It is possible that, as
prophetic diction delights in mingling figurative and real
language, and thus in some sort veiling the sense, so the words
“And there is no more sea” may be taken in the same sense as
the previous phrase, “And the sea presented the dead which were
in it.” For then there shall be no more of this world, no more
of the surgings and restlessness of human life, and it is this
which is symbolized by the sea."
Perhaps such passages in the writings of St. Augustine reflect that ancient fear of the sea that Peter Brown mentioned. He lived near water and used his experience of the sea to explain life, sin, death, salvation and eternity. His references to the sea reflect the perils of fourth century sea travel, as seen in these passages.