4 5 . 2 3 ▁square ▁kilometres . ▁ ▁History ▁▁ ▁Ch eng hai ▁was ▁known ▁as ▁one ▁of ▁" E ight ▁Count ies ▁of ▁Cha oz hou " ▁() ▁in ▁Q ing ▁D ynast y ▁and ▁Republic ▁of ▁China ▁period . ▁It ▁was ▁founded ▁as ▁a ▁county ▁in ▁ 1 5 6 3 ▁AD , ▁combining ▁by ▁the ▁coast al ▁lands ▁separated ▁from ▁H ai y ang ▁County , ▁J ie y ang ▁County ▁and ▁Ra op ing ▁County , ▁and ▁under ▁Ch ao ▁Pref ect ure ▁( Te och ew )' s ▁juris diction . ▁The ▁name ▁Ch eng hai , ▁meaning ▁" clear ▁[ the ▁W ok ou ▁of ] ▁the ▁sea " ▁( ), ▁was ▁used ▁as ▁the ▁county ▁name ▁due ▁to ▁the ▁J ia j ing ▁w ok ou ▁ra ids , ▁which ▁also ▁indicated ▁the ▁reason ▁of ▁Ch eng hai ' s ▁establishment . ▁Ch eng hai ▁was ▁dissol ved ▁in ▁ 1 6 6 6 ▁when ▁K ang xi ▁Emperor ▁b anned ▁on ▁foreign ▁trade ▁but ▁re - f ounded ▁seven ▁years ▁later . ▁ ▁In ▁ 1 8 6 0 , ▁Sh ant ou , ▁which ▁li ed ▁in ▁the ▁south west ▁of ▁Ch eng hai , ▁was ▁opened ▁for ▁foreign ers ▁and ▁became ▁a ▁trad ing ▁port ▁according ▁to ▁Tre aty ▁of ▁T ient sin . ▁Sh ant ou ▁separated ▁from ▁Ch eng hai ▁and ▁became ▁a ▁city ▁in ▁ 1 9 2 1 . ▁Then ▁Ch eng hai ▁County ▁was ▁admin ister ed