Complex sentence: Following the arrival of the Legio XX Valeria Victrix at the end of the 1st century the walls were reconstructed in sandstone, and building work continued, with interruptions, until the Roman circuit of the walls was completed over 100 years later.
Split into simpler sentences: Following the arrival of the Legio XX Valeria Victrix at the end of the 1st century, the walls were reconstructed in sandstone. Building continued, with interruptions, until the Roman circuit of the walls was completed over 100 years later.