"The workers are forced to build a big palace."

Translation: Arbejderne er tvunget til at bygge et stort palads.

[AnnabelBra4]

Why is this 'til at' rather than just 'at' or 'for at'? I just can't get my head round which version of the infinitive to use, and DL is no help, because it never tells you the rules!

[FaVX6YkH]

Arbejderne er tvunget til at bygge en stor palads?