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.
-------
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.