Near the end of his life, Roger Williams, Rhode Island founder and father of American religious freedom, scrawled an encrypted essay in the margins of a colonial-era book. For more than 300 years those shorthand notes remained indecipherable...

...until a team of Brown University undergraduates led by Lucas Mason-Brown cracked Williams' code after the marginalia languished for over a century in the archives of the John Carter Brown Library. At the time of Williams' writing, a trans-Atlantic debate on infant versus believer's baptism had taken shape that included London Baptist...