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| Isthmian Gate ... Robinson, H. S ... Depicts the following; Plan; State NB 239, pp. 103-106 ... 1962 |
| Isthmian Gate, towers I, II and III ... N/A ... Depicts the following; Plan; State NB 239, pp. 103-106 ... N/A |
| Trench(es) I ... Shelly, J. W. and Pensche ... Depicts the following; Elevation; State ... N/A |
| Trench(es) I and II ... Shelly, J. W. and Pensche ... Depicts the following; Plan; State ... N/A |
| Trench(es) IV, V, VI ... Shelly, J. W. and Pensche ... Depicts the following; Plan; State ... N/A |
| Trench(es) IX ... Shelly, J. W. and Pensche ... Depicts the following; Plan; State ... N/A |
| Trench(es) key plan ... Shelly, J. W. and Pensche ... Depicts the following; Plan; State ... N/A |
| Trench(es) VII ... Shelly, J. W. and Pensche ... Depicts the following; Plan; State ... N/A |
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