John Calvin on Isaiah 19:5

5. Then the waters shall fail from the sea. He follows out the subject which he had already begun, that the fortifications, by which the Egyptians thought that they were admirably defended, will be of no avail to them. They reckoned themselves to be invincible, because they were surrounded by the sea, and by the Nile, and by fortifications; and historians tell us that it was difficult to gain entrance to them, because the Nile had no mouth, by which they could not easily prevent ships from landing. They therefore boasted that their situation was excellent, and that they were strongly fortified by nature, in like manner as the inhabitants of Venice, at the present day, think that, in consequence of being surrounded by deep ditches, they are impregnable; but fortresses are useless, when God has determined to punish us.