The third in Skirmisher Publishing's series on fortifications and construction focuses on small fortified structures, such as might be used to guard one end of a bridge, and on "moathouses". The latter are defined as regular buildings surrounded by a wall and moat, which means that (houses having been covered in the previous volume) this is really about curtain walls.
There are 18 pages in total, three of which are splash art, and two cover contents and credits, leaving 13 pages of content (including a 1-page map). The first two pages cover the basics of the series, and are duplicated from previous volumes, but, even if you want to discount that, $2 for 11 pages isn't bad. After that, there is a general discussion of the role of the two building types described. There is some repetition here, but, in general, it's a useful checklist of things to think about - one of the main purposes of the series.
In general, the standard of proofreading is very high, and the format of the book is, like others in the series, well done, with minimal use of printer-hungry colour. The book at one point refers to "chapters" it doesn't have (it means the other volumes in the series), and, on one page, the header incorrectly states that this is volume 2. Otherwise, there's little to complain about here, and there are less such issues than there were in volume 2 itself.
Once again, this is not a book of floorplans. The final section of the book describes the curtain wall and attending fortifications around a (presumably otherwise unfortified) manor house, but the intent is to describe an example of the design of such a place, rather than to provide quality battle maps. Colour maps are included, but they're very basic, and not wholly to scale (2' thick walls are shown as about 6" thick on the maps), and are intended only to show the general layout. The plan of the pillbox shows the arrow-slits, which is useful for a defensive structure, but it might have helped if the plans of the towers did the same.
Considering that they're only protecting a manor house, not a full-blown castle, the walls are pretty impressive, but, aside from that, they're much more plausible than the inn in volume 2. For example, they're (just) within the upper range of real castle walls for thickness, and fair enough for a fantasy setting.
In summary, this is a useful booklet that achieves what it sets out to do, and that could be of use to somebody thinking about the basics of fortification. Although there are still some issues, it also shows a noticeable improvement over volume 2.