Full text: Transactions of the Symposium on Photo Interpretation

itself, are necessary. Old maps are usually the primary source of information, 
but this may be completed, or added to, by further details obtained from aerial 
photographs. Many instances of old maps and aerial photographs supplement 
ing each other can be cited. 
A 19th century map shows the site and situation of the castle of Selwerd 
(Groningen), which disappeared long ago. An aerial photograph of the site 
as indicated on the map does indeed show traces of a castle, but with a different 
lay-out from that on the map. 
The reverse is also true. One of the first K.L.M. photographs, taken in 1922, 
shows a circular mark within the modern village of Overschie. A superficial 
investigation suggested that this was possibly the remains of a, so far unknown, 
round castle. Further study of an old map indicated that, in all probability, 
this was the site of the former castle of Rodenrijs. 
The vertical photograph of the castle of Ooy (near Ubbergen) shows a 
circular ditch enclosing a round island on which stood a square tower. Inside 
this former tower there is a white dot. What is the explanation of this? In the 
fields there is little more to be seen than the slight ridge which is the remains 
of the bank of the moat. The difference in colour of the grass, which indicates 
the former position of the tower, is caused by the material used for its con 
struction. This material was tuff, which has resulted in there being richer soil 
within that limited area. It could be deduced that the dot in the centre of 
the tower indicates the foundation of the column which supported the vault. 
A drawing of the castle, made while it was still prosperous in 1736, may be 
produced as evidence in support of this deduction. 
Aerial photographs can be useful in the study of castles in various ways. 
They will be considered in greater detail and will be illustrated by examples. 
Discovery of lost objects 
Spectacular examples can be given of unknown castles being discovered, and 
of others lost in oblivion being redicsovered, from aerial photographs. There 
are few remains of very old castles, nor are there written records. However, in 
the fields their earthen ramparts and their moats left traces, which are visible 
from the air because of differences in water absortion. The former director of 
the Topographical Service in Delft, C. A. J. von Freitag Drabbe, discovered 
many, including the fortification of Blankeweer (Groningen), a round “terp” 
(artificial mound), enclosed by a double moat. 
A great success was the rediscovery of the round castle of Kuinre, when the 
Noord-oost Polder (part of the former Zuyderzee) was reclaimed. A castle, 
which was known to have been situated here, was discovered immediately. 
However, the aerial survey of the new polder, carried out after it had been 
drained, brought to light a second castle, also with a round plan and situated 
opposite the first (fig. 1). This confirmed the mention, in chronicles of 1331, 
of the “aide bergh” (old mound), which suggested that there should also be

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