Utvrda Posert (Posrt, talijanski: Possert), također poznat kao Šabec (Schabez) i Sveti Martin, ruševna je tvrđava uz cestu između Paz i Šušnjevica u općini Cerovlje u Istri. Ruševine dvorca, ovisno o imenu, datiraju iz 11. stoljeća (Sveti Martin) ili 16. stoljeća (Šabec), dok su arheološki dokazi od druge polovice 14. stoljeća. Dvorac je bio devastiran u Uskokovom ratu (1615-17). Između 2009. i 2014. dvorac je obnovljen. U neposrednoj blizini dvorca nalazi se i mala crkva sv. Martina iz 1367.
Posert Castle (Posrt, Italian: Possert), also known as Šabec (Schabez) and St. Martin, is a ruined fortress near the road between Paz and Šušnjevica, in municipality of Cerovlje, in Istria, Croatia. The ruins of the castle depending on the name are dating back to the 11th century (St. Martin), or 16h century (Šabec), while by archeological evidence to the second half of 14th century. The castle was vastly devastated in the Uskok War (1615–17). Between 2009 and 2014 the castle was restored. Nearby the castle there is also a small Church of St. Martin from 1367.