The high point of the medieval fortifications are the much-praised four city gates. They also give Neubrandenburg the nickname "City of Four Gates." Initially wooden, the connecting gates between the city's interior and the outside world were gradually replaced by the present-day brick structures at the beginning of the 14th century. Their defense was the responsibility of the four main guilds under the leadership of the four mayors, who shared the city's government during the Middle Ages. With the founding of the Duchy of Mecklenburg-Strelitz, a customs house for the princely tax collector and a gatekeeper's house were added to all four gate complexes in the 18th century: small half-timbered buildings nestled close to the fortification walls. It is noteworthy that until 1863, gate enforcement existed in Neubrandenburg. The gates were closed in the evening, and passing through the city walls was not permitted until the following morning.