Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
circum-sīdo, ĕre, v. a., to set or place one’s self around in a hostile manner, to besiege (several times in Livy; elsewhere rare): Plistiam, Liv. 9, 21, 6; 36, 13, 7; 41, 19, 10; 42, 56, 5: regem urbemque Philippopolim, Tac. A. 3, 38.