Complex sentence: Its construction commenced in 1839 and was completed in 1841 and is a replica of what is known as Pompey's Pillar in Alexandria, Egypt, which is some 10 feet lower in height.
Split into simpler sentences: Its construction commenced in 1839 and was completed in 1841. The design replicates the monument known as Pompey's Pillar in Alexandria, Egypt, which is approximately 10 feet lower in height.