Complex sentence: Excavations have discovered evidence of a major fire that destroyed most of the city shortly thereafter, but the city was again rebuilt, but by the second half of the 2nd century, Londinium appears to have shrunk in both size and population.
Split into simpler sentences: Excavations have discovered evidence of a major fire that destroyed most of the city shortly thereafter, but the city was again rebuilt. By the second half of the 2nd century, Londinium appears to have shrunk in both size and population.