The Historical Marker Database ( is an online database that documents locations of numerous historical markers in the United States as well as other countries. The database was launched in 2006 by computer programmer J. J. Prats. The HMdb served as the basis for the database for the online augmented reality game Ingress, which was then later repurposed for Pokémon Go.: 977  The HMdb was launched in 2006 with 179 markers that Prats had personally documented. By 2015 the site listed more than 74,000 markers. In addition to listing markers in the United States, the site also lists some markers from more than 40 other countries. By the start of 2018, the site documented more than 100,000 markers. More information...

According to PR-model, is ranked 5,576th in multilingual Wikipedia, in particular this website is ranked 3,119th in English Wikipedia.

The website is placed before and after in the BestRef global ranking of the most important sources of Wikipedia.

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