Sedd-i Islam - (سد اسلام; also Seddislam)
Do not mistake with Sedd-ül Islam (سد الاسلام), which is completely different fort
There are two small fortresses with the same name in the eyalet of Bosna. The primary, bigger and more important one in 17th century was in the liva of Klis1), between İskradin and İvranya. But it appears to be also part of the sancak of Kırka.2)
Location - Croatia, near Adriatic coast. Closest populated place is the town of Vrana N 43° 57' E 15° 33'map
The second fort with the same name was part of the Gabela village, close to Dubrovnik.
Location - Bosnia and Herzegovina, several km from the Croatian border. N 43° 3' E 17° 41'map
There is also a village named Islam Grcki in the region and there are some claims that the fortress was located there. Very unlikely though.
It is possible that sometimes the term sedd-i islam, which means “wall/barrier of Islam” has been used as a description for other Ottoman forts
- НБКМ Ор. 316A/190