The Maria- or Kruittoren (Behind the Vest 1) remains from the explanation of the defenses on the north and the east side, begun in 1508. It is a semi-circular lighthouse on the crown of the shore with an entrance flanked by cloister windows. The vaulted cellar served as an ice cellar in 1879 and was used by the garrison from 1892 onwards. During the restoration in 1929-30 (G. de Hoog) the top was reconstructed on the city side.
To protect the 'Houten Hoofd', built in 1464 - where the larger ships moored - the Hoofdtoren (Hoofd 2) was built in 1532-'34. This semicircular late-gothic turret tower on pentagonal substructure is covered with Gobertange and Ledesteen on the sea side and has a view on round arches. On the land side, the tower has several layers of bacon and on the north side there is a staircase tower. From 1614 to 1645 the Company van Spitsbergen was located in the upper room, to which access was changed. In 1651 the tower completely lost its defensive function. The stepped gable on the land side was then turned into a spout and a roof rider was placed with a clockwork section of ionic columns and above it two octagonal lanterns. In it hang a clock from 1522 and a clock cast by François and Pieter Hemony from 1646. The roof rider was restored in 1750 after fire. The tower was restored in 1905-'07, in 1992 and in 2003-'04.
The Oosterpoort (Kleine Oost 41) replaced in 1577-'78 the more ancient Oude Oosterpoort (demolished 1818). The gate has a completely sandstone façade on the field side and is fitted with natural stone bands on the city side. Three star vaults cover the slightly curved passageway. The rich Mannerist design is attributed to Joost Jansz Bilhamer and is determined by Doric pilasters and natural stone bands with wells. The frieze on the land side contains a Latin inscription from Psalm 127: 1. In 1601 the gate was raised with a guard house with a roof rider. The masonry arch bridge with wrought iron fences dates from 1763. The gate was restored in 1876 (A.C. Bleijs) and 1913.
In 1843 the fortifications were changed into parks. In the vestigial part (Hoge Vest) this was done according to plans by K.G. Zocher. The eastern part, which was modified around 1860, contains an aviary with a wooden house (Pakhuisstraat approx. 1950). The northern part of the moat was filled in around 1880 (Noorderplantsoen).
