MariaDB [test]> create or replace table t3( id int, row_start bigint as row start, row_end bigint as row end, period for system_time (row_start, row_end) ) with system versioning;

ERROR 4108 (HY000): `row_start` must be of type TIMESTAMP(6) for system-versioned table `t3`

It took me a while to figure why it wasn't accepting my explicitly defined BIGINT and insisting on TIMESTAMP instead; it turns out that I've actually missed UNSIGNED. While I understand that the server can't guess what the user implied, maybe it could be made better somehow.