The written heritage is the most reliable source of history of every nation and country and the basis of national identity. ERIBMWH provides digital research resources and tools for studying Bulgarian Medieval written heritage in terms of: diachronic linguistics, literary history, Bulgarian and European history, theology, cultural history and philosophy. The Old Bulgarian language (Old Church Slavonic), created by the Holy Brothers Cyril and Methodius, functioned as a sacred language of all Orthodox Slavs in Southeastern Europe during the Middle Ages. That is why researchers interested in the history and culture of the Slavo-Byzantine Medieval word are using the RI. The introduction of digital technologies in such a conservative field as historical humanities not only optimizes the work of researchers but also creates the conditions for new research initiatives and projects.

The electronic research resources and tools for processing medieval texts of proven Bulgarian origin have been created for 10 years through a series of scientific and educational projects. The Histdict system is currently part of the Cyrillomethodiana web portal and consists of the following resources and tools:

• Diachronic corpus of Bulgarian language 9th-18th c. (150 texts from different genres and in original spelling)
• Digitized Old Bulgarian Dictionary (10500 dictionary entries)
• Reverse Greek-Old Bulgarian Dictionary
• Historical Dictionary of Bulgarian language (a developing resource of diachronic type)
• Synchronous Historical Dictionaries: Dictionary of the Language of Partriarch Euthymius; Terminological Dictionary of John the Exarch
• Specialized software for writing and editing dictionary entries
• Grammar dictionary and semi-automatic morphological analyzer
• Search engine and virtual keyboard
• Old Bulgarian Unicode fonts and converter

The open access Histdict system is a complex of unique resources and tools for publication and research of medieval Slavonic texts and in a European and global context is corresponds to Thesaurus Linguae Graecae and Perseus, representing the classical written heritage.