Varchar to DateTime conversion Error

Hi,
select CAST('1600-01-01 00:00:00.000' as date) => works fine but below query fails
select CAST('1600-01-01 00:00:00.000' as datetime)   got an error:
Msg 242, Level 16, State 3, Line 1 The conversion of a varchar data type to a datetime data type resulted in an out-of-range value.

Any reason for failure?
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