10 amazing medieval towers and defenses in Bulgaria.

http://www.vesti.bg/lyubopitno/puteshestvia/10-udivitelni-srednovekovni-kuli-i-ukrepleniia-v-bylgariia-6056741

border line and defenses during 80's
http://e-vestnik.bg/5932

the new border line with Turkey - first half of 21's century
http://www.nytimes.com/2015/04/06/world/europe/bulgaria-puts-up-a-new-wall-but-this-one-keeps-people-out.html?_r=0