C for Calendar

The history of calendar can be read through these links:

https://www.thepatriots.asia/sejarah-penciptaan-kalendar-masihi-sistem-rom-julian-dan-gregorian/

http://pmr.penerangan.gov.my/index.php/penafian/1614-ingin-tahu-info-terkini/berita/12047-asal-usul-kalendar

http://www.ustazusa.com/2016/12/sejarah-kalender-masihi-satu-kajian-awal.html

The information in these articles are amazing.