Hello again, Jessie,
"The" is needed there. We don't say say things like "on twelfth of March"; we say "on the twelfth of March." You can also say:
- on March twelfth
- on March the twelfth
- on 12 March 2019
The second option ("on March the twelfth") is the most formal and old-fashioned. The construction isn't used much nowadays, but I like it.