24 June 2015. With Kurdish fighters (and FSA) advancing to up to 50 km from Raqqa city, which is Isis' headquarters in Syria and the 'capital' of the caliphate, the Islamic State is said to be hurriedly building concrete walls in the northern part of the city to defend their territory.

INTERNATIONAL BUSINESS TIMES

http://www.ibtimes.co.in/syria-isis-builds-walls-raqqa-kurdish-ypg