The Poznan Project – Poznan Region Marriage Indexing Project for 1800-1899 is a valuable tool for those who have ancestors who lived in the Poznan (formerly Posen) region in what is now Poland. According to Wikipedia, the Province of Posen was a province of Prussia from 1848 and as such part of the German Empire from 1871 until 1918. It had an area of 11,185 mi².
Here is a sample Poznan Project Search Results Summary when searching for marriages of persons with the “Heins” surname, showing 15 matches found in 21.99 seconds:
Here is a representative sample of the results of the search on the “Heins” surname:
Map of the former Prussian Province of Posen on Wikimedia Commons. Scroll cursor over image for attribution.