循 circulate

Guards armed with shields go and circulate around the city.

a vicious circle. ★☆☆☆☆ NEO
悪 (bad) + 循環 (circulation ) = 悪循環 (a vicious circle.)

circulation ☆☆☆☆☆
循 (circulate) + 環 (environment) = 循環 (circulation )

circulation - whether blood, air, whatever.