Mediaeval Spanish texts display a range of constructions which are formed by a present, past or future tense of the verb haber and the past participle of a transitive verb. In these constructions the direct object may precede or follow the participle; the participle sometimes agrees with the object, sometimes not: las batallas (que) ha vencidas/vencido, ha vencidas/vencido las batallas. During the thirteenth century an alternative type—tener +past participle—begins to appear with increasing frequency; it regularly indicates a state and, where tener is used, it is standard practice for past participle and direct object to agree: la tienen cercada, los tenie atributados. It is generally accepted that agreement is particularly favoured in the north-eastern dialects of the peninsula, but to the best of my knowledge no systematic attempt has been made to account for the syntactical, historical or geographical factors which affect past participle agreement in Old Spanish.