FromDigits

FromDigits[list] constructs an integer from the list of its decimal digits. 

FromDigits[list,b] takes the digits to be given in base b. 

FromDigits[list,MixedRadix[blist]] uses the mixed radix with list of bases blist. 

FromDigits["string"] constructs an integer from a string of digits.

FromDigits["string","Roman"] constructs an integer from Roman numerals.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.