I can remember Francis detesting the thought of the U.S. building a wall when it was pointed out that the Vatican has an immense wall surrounding it that has been standing way longer than the U.S. has existed.

Indeed, the latter wall is the famous Leonine Wall: the namesake project of Pope Saint (ahem!) Leo IV (A.D. 847--855) [*].

Which makes that wall more than a century older than the archæological site, in modern coastal Canada, that's proof of any settlement in North America by any Europeans, in this case a Scandinavian expedition seeking "Vinland" (~1000).  And 7 centuries older than San Agustin (1565): the oldest permanent settlement in the future continental U.S.A.

The Vatican Hill is on the wrong side of the Tiber to have been enclosed in any of the wall-building projects decreed or sponsored by Roman Emperors.

Alas, no later than A.D. 846, when the Mediterranean had become practically a Saracen lake, Saracen raiders [☪] had learned that there was wealth worth taking outside the imperial Roman walls: Wealth that had been accuмulated there by a successful religious organization, which had been free of persecution for 1/2 millennium.  Pope Sergius II (844--847) had no viable defenses against those Saracens when they rowed a fleet of boats up the Tiber that year, and sacked Old St. Peter's Basilica and St. Paul's Outside the Walls.

In the following year, Leo IV was elected to the Chair of St. Peter, and must've made some kind of promise--if not a formal oath--to the effect "Never again!"  So he led a hike around the unprotected perimeter of the Vatican, much like a Rogation Day procession, except that the location of his footsteps was recorded.  Then he decreed that a defensive wall be built along his footsteps.  Altho' Rome then existed in the "reduced circuмstances" of the mere Duchy of Rome, Holy Roman Emperor Lothair (r. 843--855) contributed substantially, as did cities and the proprietors of various properties in the duchy.  While the wall was still under construction, Saracens attempted another raid, but before they could enter the river, they were sunk or dispersed by a "tempest" (849).

The wall was completed in 852, and solemnly blessed by Leo.  There must have been substantial Grace from God speeding not only that project, but also the surprisingly numerous additional defensive or restoration projects of Leo, because the royal agreements known as the Treaty of Verdun (843) [×] had provided a period of peace among the royal contenders who were foolishly fighting over the succession and territory of the Holy Roman Empire.  This was wasting money & manpower urgently needed elsewhere, e.g., the empire's northern lands, which were also under attack, but from Vikings.  In the year after the wall was completed, the restraining power of the treaty faded away [×].

The 3rd time that Saracens attacked Rome (perhaps after Leo's death, the attack not being mentioned in the cited article [*]), they were defeated by Roman defenders.

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Note *: Horace Mann. "Pope St. Leo IV".  The Catholic Encyclopedia, vol. 9.  Robert Appleton Co.: New York, 1910. <http://www.newadvent.org/cathen/09159a.htm>.

Note ☪: In ancient times, "Saracens" referred to (desert) bedouins, presumably ethnically Arabs.  By mediæval times, it referred specifically to Arab Muslims--practicing that unconvincingly alleged "Religion of Peace"--engaged in brigandage, piracy, and occasionally in more disciplined actual military operations.  Let's not forget that those operations were conducted mostly against predominately Christian populations and states, notably the Byzantine Empire.[♠]

Note ♠: Aside from all that, it seemed highly likely to this member of CathInfo that the eastern "Saracen Lake" was actually Berber-majority (Greek Mauroi, then Latin Mauri, English "Moors") instead of Arab-majority.  But trying to confirm that, this member was overwhelmed by an avalanche of unfamiliar names, which is not an appealing way to spend multiple hours on a summer week-end day whose forecast thunderstorms haven't yet arrived.  It does seem that the occupation of Sicily, which was begun at Mazara by "Moors" in 827, had originated from Tunis and Algiers.  Certainly, the Muslim conquest of the Iberian Peninsula (i.e., Spain & Portugal) had been carried out primarily by Berber Muslims, and despite the dynastic and ethnic in-fighting, Muslims had held most of that peninsula for most of a century by the time of Pope St. Leo IV.

Note ×: The Treaty of Verdun is far more than a sidelight on the projects of Pope St. Leo IV; it was a major event in the history of mediæval Europe, and in the shaping of modern Europe.  Alas, The Catholic Encyclopedia seems not to have any articles dedicated to the treaty nor, more surprisingly, to the Holy Roman Empire, nor its Emperors Lothair or (his son) Louis II.

I haven't hea[r]d about any plans to tear down the Vatican's wall.

It would be imprudent--if not downright foolish--to "tear down that wall",  given masses of alleged "refugees" entering southern Europe--including Italy--who are disproportionately young men, amazingly fit & trim and freshly clothed & shod, who look more like active-duty military on annual leave.  Yet sympathetic readers in the U.S.A. are self-righteouly led to expect to see women & children, obviously nearly starvation, and clothed in disintegrating rags.

It could be great fun to watch the twitter feathers fly if "Pope Francis" publicly makes an issue of the labor and other resources used to build the U.S. southern-border wall.  Because history records that the Leonine Wall--that wall around the Vatican--was built by Saracens who were captured during their raids, then put to work as slave labor, according to the customs of the times--even those of the Church.

I wonder if any of those captured Saracen invaders were ever "reünited with their children", or assigned a date for court, then released into the population they'd invaded, hmmm?

Attributing a moniker of a criminal nature to a saintly person, is just wrong.

Doing the Will of God is not criminal.

If I saw a Mexican drowning as he was swimming across the Rio Grande to enter the U.S. illegally or one stranded in the desert after crossing into the U.S. illegally, I would try to save them as perhaps the so called "Coyote [unusual name assignment since it is the slang name given to one who illegally smuggles people across borders of countries]  Saint" would do.

After I did that, on the other hand, I'd try to notify "La Migra" (the border patrol) so they could take them into custody.  I have no idea if the "Coyote Saint" would do that as well, although I kind of doubt it.  In any event, the border patrol if they share the same patron saint (St. Michael the Archangel) as police officers could certainlly thank St. Michael for helping to apprehend those who are supposedly helped from being apprehended by the "Coyote Saint."