On the night of October 6, 1810 the growing town was faced with a disaster, a fire broke out. Three quarters of the town was destroyed, ie. about 60 houses, including the town hall with its records. The church, the schoolhouse, a few houses in Rantakatu and some small dwellings on the north side of the church hill were saved.

The commission surveyor Gustaf Odenwall was assigned to draw up a new town plan and a plotting-out plan for rebuilding the town. The burghers and the town administration had agreed upon certain principals concerning the rebuilding of the town and the new plan, such as:

• A new, larger market square would be opened at the corner of Isokatu and Kirkkokatu.
• The streets would maintain their previous width, the idea of widening the streets for purposes of fire safety was given no support.
• A space of three cubits or about 1.5 - 2 meters would be left unbuilt on the boundaries of the plots for tire safety purposes.
• Due to the enlargement of the plots, also the town needed to be extended.
• Two-storey wooden houses could not be built anymore, the stone base could not be too high, the buildings and their stone bases facing the street were to be of a uniform height.