1. Add sugar, water, cinnamon, anise, cloves, orange peel, and the orange slices a to a pot and heat gently until the mixture becomes syrupy.
2. Cool completely, then pour into a jar and add the gin.
3. Shake well to mix, and store for a week, minimum.
4. Fill up a rocks glass with ice cubes.
5. Strain in the infused gin, Campari and sweet vermouth in a cocktail shaker and pour over the ice.
6. Garnish with an orange slice.