Ostrog is a Russian term for a small fort, typically wooden and often non-permanently manned. Ostrogs were encircled by 4–6 metres high palisade walls made from sharpened trunks. The name derives from the Russian word строгать (strogat'), "to shave the wood". Ostrogs were smaller and exclusively military forts, compared to larger kremlins that were the cores of Russian cities. Ostrogs were often built in remote areas or within the fortification lines, such as the Great Abatis Line.