Complex sentence: Sidi Barrani is often mentioned, in historical terms, to denote the extent of the initial Italian invasion into Egypt, from Libya, and the Italian Tenth Army would build a series of forts in the vicinity of Sidi Barrani.
Split into simpler sentences: Sidi Barrani is often used, in historical writing, to mark the extent of the initial Italian invasion into Egypt, from Libya. The Italian Tenth Army would build a series of forts in the vicinity of Sidi Barrani.