Architectural historian. Died aged 57.

Di Stewart was a passionate and feisty defender of Auckland's heritage buildings and the author of the definitive book on New Zealand villas.

She played a huge role in saving the historic buildings in the Britomart development. The original Britomart proposal planned to raze most of the notable buildings in the precinct and to sink Quay St into a tunnel where pedestrian use was heaviest.

This scheme first came to public notice during a Christmas period when obviously its proponents hoped no one was noticing. Stewart was horrified by the scheme and, supported by a number of heritage activists, architects and planners, put huge energy into opposing it.

A more appropriate scheme was devised which saved most of the buildings.

Stewart worked for 20 years in the heritage conservation field in New South Wales and New Zealand. She got on equally well with developers, politicians and heritage campaigners.

An activist campaigner, she would swing into noisy action, getting the Minister for Conservation at the time to sign protection notices to save Auckland buildings such as the Bluestone Store, the BNZ facade, Courtville Apartments, the Civic Theatre and the upper Queen St shops.

When she returned to New Zealand in the mid 1980s after working for the National Trust of New South Wales, she castigated Ponsonby friends for allowing the construction of two high-rise apartment buildings on the Jervois Rd ridge during her absence.

In 1986 Stewart was appointed the first Auckland Regional Officer of the Historic Places Trust and set up its first Auckland office.

She played a leading role in introducing concepts that have since become the norm in New Zealand conservation plans, such as heritage studies for town centres.

After leaving the trust she worked in private practice as a heritage consultant and architectural historian. She prepared numerous conservation plans and heritage studies for places such as Thames, Wanganui, and Ponsonby Rd.

Stewart's book, The New Zealand Villa, Past and Present (Viking Pacific 1992), was hugely popular and was republished last year.

She was a strong advocate of the Mainstreet programme, a partnership between local government, the business community and the wider community to preserve heritage buildings and build liveable communities.

For the past three years she was a community planner for Mainstreets for the Auckland City Council, responsible for the management of 16 Mainstreet programmes in the city.

She also had a special affection for Ponsonby, where she lived for much of her adult life. In 1996, Auckland City commissioned Stewart and architectural and conservation consultant Bruce Petry to produce a three-volume heritage study on Ponsonby's historic buildings and places.

This was incorporated into the 1999 District Plan as the Ponsonby Centre Plan, aimed at conserving the vitality and heritage of the Ponsonby/Jervois Rds ridge precinct.

She is survived by her parents, sister Alice, and children Mary, Kate and Tim.