DIEZ, town of Hesse-Nassau, Prussia, Germany, in the deep valley of the Lahr', crossed by an old bridge, 3o m. east from Coblenz on the railway to Wetzlar. Pop. 3,309. It is over looked by a former castle of the counts of Nassau-Dillenburg, now a prison. Close by, on an eminence above the river, lies the castle of Oranienstein, formerly a Benedictine nunnery. The industries include iron works, machine-making, colour preparation, lime-burning and quarrying. In the vicinity are Fachingen, cele brated for its mineral waters, and the castle of Schaumburg.