BLOCKZIEL, a fortress of Overijssel, in the Netherlands, seated on the river Aa, at its junction with the Zuyder Zee. It has a port sufficient to contain 200 vessels, and serves to defend those ships that cross the sea. Its fortifications, which were considerable, have been allowed to fall to decay. The trade of the town is extensive. Long. 5. 52. E. Lat. 52. 45. N.