caput draconis ultimum

hello! I am a medieval history student only just starting learning Latin and sadly not skilled enough to translate things and know they are going to be correct. if anyone could help me with this poem attributed to Gregory IX in the 13th century that would be great!

Caput draconis ultimum

Ultorem ferens gladium

Adversus Dei popular

Excitat bellum septimum

Contra coelum erigitur

Et nitiur attrahere

Maximam partem siderum

Ad damnatorum numerum

Verum de Christi latere

Novus legatus...

caput draconis ultimum