Why preceding length field is required while creating Fields in Data base dictionary with type LCHAR or LRAW

Hello ABAP Guru's

I am trying to create table Fields With giving the Data type as LCHAR or LRAW in se11..It is giving error like ' Z<Field> does not have a preceding length field of type INT4'

and when I created another field (above to LCHAR or LRAW field ) with data type with INT4 is not showing error.

Please let me know what is the reason behind of this....

Thanks In Advance,

Sekhar