The city was first documented in 1332 in the papal registry under the name Novum Forum Siculorum, and as Sekulvasarhel (Szekelyvasarhely) in 1349. On the place of its Castle Church, the Dominican’s church stood until the Mongol invasion, when it was destroyed. In its place, the Franciscans built a new Gothic church in 1260, which was completed in 1446. Since 1439 the town was the scene of the session of parliament (diet) 36 times.
In 1405, the King of Hungary Sigismund of Luxembourg granted the city the right to organize fairs. In 1470 King Matthias Corvinus granted the first judicial privilege to the city, and in 1482 declared the city a royal settlement. In 1492, wayvoda Istvan Bathory strengthened its monastery with fortifications, this was a pentagon-shaped outer castle tower.
In 1506, the troops of Pal Tomori were beaten by the Szeklers rising
against the payment of an extraordinary Ox tax imposed on them on
occasion of the birth of Louis II of Hungary. In 1557, the Reformed
Church College (i.e. Presbyterians) was established as the oldest
Hungarian school of Transylvania. In 1571, the session of Transylvanian
parliament under prince John II Sigismund Zapolya accepted the free
preach of the word of God, including the Unitarian Church.