Pictures of buildings mentioned in the second edition “Suffolk” volume of “The Buildings of England” series by Sir Nikolaus Pevsner.

For the time being just two entries for Felixstowe from the end of the entry in Pevsner. "Towards the S end of Felixstowe two military oddities: Martello Tower, S of beach Station. Built c1810-12 (cf. Aldeburgh, p73). One of several."
The Aldeburgh entry adds "The Martello Towers were built in 1810-12 by the royal Engineers as a defence against a Napoleonic invasion. They were designed by Colonel Twiss and Captain Ford. The name comes from a Torre della Martella in Corsica which impressed the English in the campaign of 1794".
Here are two of them at the Felixstowe Ferry end of the town:
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The second "military oddity" is "Landguard Fort, near Landguard Point to guard Harwich Harbour. First built in 1540-5. Rebuilt in 1624 etc. as a square with square angle bastions. Again rebuilt in 1717-20 as a low polygon of red brick with angle bastions. In this form the fort remains, though the archway is Victorian, as is the whole interior with its circular building and circular courtyard. That is dated 1875." Here are several views of it:
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Some of the walls:
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And the main entrance:
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