Only a few fragments of the 4th-century walls remain; for example, the original Roman wall is visible on the southern boundary of the parish church of St Peter and St Paul. The area occupied by the fortress is now classified as a Scheduled Ancient Monument. The church of St Peter and St Paul, which is enclosed within the fortress, has an Anglo-Saxon tower. The market square lies at the heart of a conservation area which contains 56, mainly Grade II, listed buildings. In numerical terms, the number of listed buildings makes Caistor the most important conservation area in the West Lindsey area; many of the buildings are Georgian or Victorian. Notable buildings in the town include Caistor Grammar School, founded in 1633, and Sessions House, built in 1662.