Fortified religious buildings

St. Andrew's Church, "A Rare Surviving Example Of The European Fortress Church Used For Defensive Purposes" (Wiki)

St. Avit Sénieur In The Dordogne

"At Ávila The Cathedral Was Incorporated Into The City Wall" (Wiki)

"The Churches Also Served As Forts In The Earlier Years Of The City."

Cathedral: "Durham Cathedral Was Also Partly Fortified And Known As 'Half Fortress Against The Scot'."

Monastery

"These Monasteries Were Built Very Solid With Thick Walls And Very Austere. In Some Of The Complexes, One Can See Stone Merlons Which Make The Complexes Look Like Castles Or Forts. These Were For Defensive Purposes As The Monks Were Invading Mesoamerican Lands To Impose A New Religion. For This Reason, Churches And Monasteries Of This Type Are Called "Fortress Temples." (Wiki)

"The Entire Guarding And Defending System Was Pointed Towards The Enemy Coming From The Sea. He Came Up Against The Fortification Of The Shore (Fortified Harbors And Towers), Then Against The Fortifications Of The Monasteries That Could Held Out Until The Outside Help Arrived. During The Ottoman Domination There Was An Army Body To Protect The Monasteries."
See Forum.Boinaslava.Net

Weissenkirchen Church
See Www.Tourmycountry.Com

Nuestra Senora De La Asuncion In Santa Maria
See Www.Wmf.Org

Sergiev Posad - The Whole Complex Is Protected By Fortress (Posad In Russian Means Fortress)

The Whole Complex Is Protected By Fortress-Like Wall

The Upper Complex Is Protected By High Wall Similar To The Beijing's Forbidden City

Hulterstad, Remso

The Spaso-Preobrazhensky Monastery In Yaroslavl Was Built To Be A Citadel In Times Of War. The Monastery Is Surrounded By A Thick 16th Century, White-Painted Wall, Complete With Watchtowers And Embattlements.

Fortified Church In Oberwesel

Each Citadel Has A Fortress-Like Mosque, Whose Minaret Served As A Watchtower.
See En.Wikipedia.Org

Fortified Church Of Santa María In Tobed

The Monastery Of Santa María La Real De Nájera, Home To The Navarran Royal Mausoleum Is A Classic Example Of A Fortified Church And An Important Stop On The Camino De Santiago In Spain. "The Exterior Of Santa María La Real Shows Characteristics Of A Fortified Building...Defensive Needs Led To High Walls And Buttress With The Function Of Bastions" (Wiki)
See En.M.Wikipedia.Org

"The Tall Towers Of The Churches Served Both To House The Bells And To Act As Lookouts In Case Of Attack. Alongside Each Of Them Is The Walled Village Cemetery. The Three Belltowers Of Boí, Taüll, And Erill La Vall Are Intervisible, A Notable Defensive Feature." - Ab Evaluation