“A person who thinks only about building walls, wherever they may be, and not building bridges, is not Christian,” Pope Francis declared on his flight back to Rome last week.The political implications of his statement have been considered in some detail in recent days, but his assertion also needs to be examined in the light of history.

Had it not been for the walls, strongly built and staunchly defended, Christendom would not have survived the onslaught of Islam in its thousand-year-long period of military expansion. Two prominent examples come from the final two centuries of that period: the sieges of Vienna in 1529 and 1683. The first marked an important early check on Turkish advances, after a century of conquest in the Balkans and Central Europe. The second saved Europe and finally turned the tide. German, Hungarian, Polish, and other defenders of the walls of Vienna were Christian warriors par excellence. During the second siege the city was saved thanks to an alliance between the Holy Roman Empire and the Kingdom of Poland, which was brokered at the last minute by Pope Innocent XI. In thanksgiving for the victory at Vienna on September 12, 1683, Pope Innocent fixed that date as the Feast of the Holy Name of Mary.

Over two centuries earlier, in July 1456, some 6,000 Christian soldiers successfully defended the walls of Belgrade from Sultan Mehmed’s army of 50,000. During the siege Pope Callixtus III ordered the bells of all churches to be rung every day at noon, as a call for believers to pray for Belgrade’s defenders; that practice has continued to this day, even though not many people know its origins. An old Franciscan monk and preacher, John of Capistrano, played a key role in the battle and personally led a detachment of troops. For his valor and burning faith Pope Alexander canonized “the soldier priest” in 1690.

In 1565 the walls of the Grand Harbor in today’s Valetta enabled 700 Knights Hospitaller, 2,000 Spanish and Italian soldiers, and 4,000 armed Maltese civilians to withstand an assault by 50,000 Turks and North African corsairs. The 70-year-old Grand Master of the Order of St. John, Jean de la Valette, commanded the garrison. “It is the great battle of the Cross and the Quran which is now to be fought,” he told his troops as the Ottoman fleet appeared on the horizon:

A formidable army of infidels are on the point of invading our Island. We, for our part, are the chosen soldiers of the Cross, and if Heaven requires the sacrifice of our lives, there can be no better occasion than this. Let us hasten then, my brothers, to the sacred altar. There we will renew our vows and retain by our Faith in the sacred sacraments, that contempt for death which alone can render us invincible.

When the arrival of a relief fleet from Italy was unexpectedly delayed, de la Valette did not lose heart. “We now know that we cannot look to others for our deliverance,” he told his Council. “It is only upon God and our own swords that we must rely. Yet this is no reason to be disheartened . . . Our Faith and the honour of our Order are in our own hands. We shall not fail!” Valette’s Christian warriors did not fail. As the battle reached its climax, they “sang Hymns, prayed, defiantly tolled their Chapel bell and prepared to meet the Lord Jesus.” The Great Siege of Malta and the Battle of Lepanto six years later marked the end of the Muslim bid for control of the Mediterranean. The Christian coalition which made that victory possible, known as the Holy League, was put together by Pope Pius V.

Besieged Christian walls occasionally became the scene of heroic last stands. In 877-78 a small Greek garrison defended Syracuse against the Saracens to the last man, even though no help could be expected after the defeat of the incoming Byzantine fleet. Emperor Constantine XI’s defense of the walls of Constantinople in 1453 is another example of willingly accepted Christian martyrdom. In 1571 6,000 Venetian defenders of Famagusta succumbed to 100,000 Turks and their 150 guns after a year’s siege. Their commander, Marcantonio Bragadin, was tied naked to a column and flayed alive while praying the Miserere and invoking the name of Jesus.

As we have been reminded in recent days, most of the Vatican is surrounded by walls that are 40 feet high and 12 feet thick. Enrico Maria Radaelli, a leading disciple of the late Romano Amerio, says that it would be interesting to know “what Pope Bergoglio thinks of the famous Leonine Walls, erected by his predecessor Pope St. Leo IV in 847 to defend Rome and the Pope’s residence from the Saracens . . . Was Pope Leo, sainted and responsible [for] many a miracle during his lifetime, not ‘a good Christian?’”

The same question may be asked regarding 82 percent of Hungarians who supported tighter immigration rules after the government of Viktor Orban built a fence along the country’s southern border last summer; or 40 percent of Polish voters, most of them observant Catholics, who supported the openly anti-immigrant Law and Justice Party at last October’s general election; or thousands of Slovaks who attended a mass rally against immigration in Bratislava last month; or thousands of Italians, mostly Northern League supporters, who gathered for the same purpose in Rome on January 28.

In June 2007 I was received at the Vatican by Mgr. (now Cardinal) Pietro Parolin, who was at that time Undersecretary of State for Relations with States. (In August 2013 Pope Francis elevated then-Archbishop Parolin to the post of Secretary of State). As might be expected, I had to pass through several checkpoints with metal detectors and other paraphernalia of strict border security. I have no reason to doubt that the friendly but efficient Swiss guards manning those “walls” and preventing the entry of uninvited strangers were good Christians.