Complex sentence: Zilantov Monastery and the Admiralty were turned to strongholds, and redoubts were installed at Kazanka's bank and Arsk Field, a system of knife-rests was installed around the city.
Split into simpler sentences: Zilantov Monastery and the Admiralty were turned to strongholds. Redoubts were installed at Kazanka's bank and Arsk Field, a system of knife-rests was installed around the city.