Historical clue formulations

• German steel city — 2026-01-21
• German industrial city — 2026-01-14
• German city in the Ruhr Valley — 2021-09-13
• German steel city — 2021-04-18
• German industrial hub — 2020-12-28
• German industrial city — 2020-03-16
• German steel city — 2020-02-17
• German industrial city — 2019-05-13
• Center of the Krupp family dynasty — 2019-04-25
• German steel city — 2018-10-29
• German steel city — 2017-11-16
• Ruhr industrial city — 2017-01-29
• Ruhr Valley city — 2016-08-30
• European city whose name means "eat" — 2016-07-08
• Krupp ironworks city — 2016-06-14
• German coal city, once — 2015-10-11
• German steel city — 2015-02-25
• Krupp Works city — 2014-11-19
• European city of 500,000+ whose name translates as "to eat" — 2014-11-06
• Scene of W.W. II airstrikes — 2014-10-10
• German industrial city — 2014-10-06
• Westphalian city — 2014-06-20
• W.W. II bomb site — 2014-04-15
• Ruhr Valley city — 2014-02-17
• Home to the Villa Hügel — 2014-02-15
• Western German city — 2014-01-09
• City on the Ruhr — 2013-12-02
• German steel city — 2013-07-29
• - — 2013-01-27
• Ruhr city — 2012-12-11
• Steel city of Germany — 2012-11-29
• City whose name means "eat" — 2012-07-14
• City north of Bonn — 2012-07-12
• City that hosts the world's biggest annual game fair — 2012-06-03
• European city whose name sounds like two letters of the alphabet — 2012-04-07
• Germany's University of Duisburg-___ — 2011-10-15
• Industrial hub of Germany — 2011-10-02
• City on the Ruhr — 2011-07-17
• Where Alfred Krupp was born — 2010-12-17
• Industrial city of Germany — 2010-12-13
• City steel in Europe — 2010-04-01
• Ruhr Museum locale — 2010-02-06
• City SSW of Münster — 2010-01-03
• City near Düsseldorf — 2009-11-01
• Ruhr Valley city — 2009-06-22
• Ruhr industrial hub — 2009-05-21
• Krupp Works city — 2009-05-11
• Ruhr Valley city — 2009-04-19
• German city whose name means "to eat" — 2009-02-08
• German steel city — 2009-01-05